Minecraft can be extremely addictive. I know from personal experience. To give you an idea, I'm a freelancer and for a large percentage of last year I was playing more hours of MC a week than I was billing clients.
You sound like you may be similar to me with games so let me lay it out for you.
When you first start playing you know nothing. There's so much to do and learn. You'll be scared of nighttime and dark caves. You won't know how to craft anything. You'll probably get killed a lot and get lost. It will suck you in for the first 30-60 hours while you learn how to play single player.
At that point one of two things happen. Either you really like building structures and you keep playing a lot or you get bored. I got bored.
Then I realized I was only experiencing a small fraction of the game. The modding community is HUGE, larger than any other game I've played. There are hundreds of mods available that expand and modify gameplay making it far more interesting than "vanilla" MC. Each mod can add 5-50+ hours of interesting gameplay.
This isn't even accounting for multiplayer, which can be much different. PvP servers with clans, mod servers with large towns, creative servers with builds that take months to complete.
I'm not saying you shouldn't play. Minecraft is a great game. Just be aware of where it can lead if you don't plan your time well. I've since cut way back and don't play games as much.
One way you can get a good feel for MC is to watch some of the popular YouTubers. I primarily watch the Yogscast but there are plenty of other good ones.
This makes the pocket and xbox edition experience quite a bit different from the PC/servers version.
My experience was I made a lair basically tunneling out an entire 100x50 ish island, built a tower going up until I was bored and a spiral staircase from top down to bedrock, then dug what amounts to a giant multi-lobed endless loop subway just above sea level around the map (probably about 4 minutes, yes that is indeed a lot of mined/smelted iron, and gold/redstone to boost my cart up to speed) diverted into optimized partially-automated chicken production, then got kinda bored. I think I got about a hundred hours of fun out of it, which, for what it costs, is an excellent rate of return.
It reminds me of an old saying about "second life" from about a decade ago, where if you can't be entranced by it for at least a dozen hours, there's probably something wrong with you, but much after a hundred hours or so, its kind of boring.
A third comparison of about equal depth and entertainment was playing Eve:Online also about a decade or so ago without joining any social groups (which was impossible because I was scavenging random hours here and there, and clans wanted dedicated scheduled mining/raiding nights and such)
All three share the characteristic that its hard to go beyond a hundred or so hours without the community, although if the community drags you in, then you're stuck in there forever.
There's probably a startup lesson in here that if you want more than 100 hours of engagement, its going to come from the community, not the programmers / artists / suits.
I've gotten to the point where I'm not sucked in and addicted to MC anymore, but since it was the building part that I got stuck on, never modding or multi-player, I still get plenty of enjoyment when I periodically think of something new to build.
(E.g. I built a residence, garden, etc. in a cloud then decided I could expand that to a several-cloud city. Then decided I could build a tower with railroad in an attempt to bring cows and pigs up there. The next project might be an underwater city, or play around with the new horse stuff they added.)
New content is added occasionally. I'm not entirely sure why, since they don't have continuous subscription revenue like WOW does. I actually find it kind of annoying since then I need to explore another huge swath of territory to get new chunks to generate with the new stuff in it. Or worse, if the new stuff breaks the timing on some of my red stone circuitry or the effectiveness of my experience generator.
Similar to the game he canned, check out Red Power 2 for MC, it's actually got an in-game computer you can program it in Forth, save programs on in-game floppies, and build a giant IO bus to control various things in the game world.
If you like games like SimCity, you might like Minecraft. Although SimCity has much deeper game mechanics, Minecraft focuses on exploration. (HN crowd: bear with me, they're b both exploratory world-building games to a certain extent with terraforming. For me personally, my enjoyment of them is the same for similar reasons.)
There are a large variety of clones out there, and "inspired" titles, but Minecraft got a lot right as far as a sense of exploration is concerned.
There's a fairly advanced open source "Minecraft-inspired" game called terasology I found this weekend:
It's not as polished as Minecraft, but if you just want to get a feel for the basic mechanics and tinker without having to pay anything, it's worth a look.
Notch doesn't maintain Minecraft himself these days; Jeb at Mojang does. But they're doing a great job.
I no longer have the time to play Minecraft regularly, but I revisit it from time to time, just like Simcity.
As a game with any purpose aside from building, it falls flat. After the first evening or two, monsters aren't a real issue unless you want them to be, exploration is somewhat dull after your first few caves, and the graphics (while arguably part of Minecraft's charm) are about as basic as you can get.
There are a number of mods and texture packs which address some of these issues to some extent or another, but even they get dull quickly.
Ultimately, it's a set of digital legos, and your enjoyment of the game will depend greatly on how much you want to play with digital legos.
Disturbingly addictive. I have those willpower problems, beware. I just downloaded it to try it and got captured. There's several modes of play, and lots of possibilities. So you keep coming back to it with what-ifs. I found something to take the magic out of the game: a no-clip tool that sees through the map shows all the caverns.
That depends on why you feel the need to keep playing a game.
Most games sort of pull you along. They want you to finish the whole thing, so there are various incentives to make you want to keep playing and progressing the game's storyline, or your character level or whatnot.
Games like Minecraft are more of an environment to push against. You keep playing because you want to finish your castle of doom or lake of lava or whatever.
Either type of game can suck you in, it just depends on your personality type. Personally, Minecraft doesn't do much for me; I'm much more vulnerable to the "just one more level" attraction of more linear games. I can't speak for you, though.
Classic mode is awesome. I haven't played in quite awhile, but there were some good servers with ridiculous amounts of awesome mods.
It runs much faster than normal Minecraft, and some of the features like cuboid, permissions, multiple maps running on the same server, etc, still haven't been added back to the main version of the game.
Because they aren't part of the game - they're server plugins, and are all available for Bukkit by now (and have been since at least Beta).
Cuboid is part of WorldEdit, there's tons of permissions plugin (PermissionsEX seems to be the most mentioned, though in both positive and negative terms) and there are quite a few MultiWorld plugins for Bukkit nowadays.
How addictive is minecraft? It sounds great. But I quit video games a few years back, and don't have good willpower with them.
I work from home as well, so there's no natural limits on my time. But I'd love to try the game in a limited way.