Yes, it's pretty secure against brute force. However if everyone start doing this, I suspect that we're going to have a lot of passwords like "I am hungry today" or even "car house hello red" which are both rather weak against an attack that would combine the most frequent words. You can't really prevent people from using common words and common patterns to build their password and hackers are going to use this fact.
So my problem is that it gives the impression to be very secure whereas it's only secure under some conditions. (You have to pick words uniformly among the list of words.) Just like old password...
You have to pick the words uniformly, yes. Thankfully, that's easy to do (rl -c 4 wordfile), and can be made easier. The point isn't "make up passwords that look like this" - it's "using this algorithm you get passwords that look like this that have this level of security[1]," and it's way easier than generating a secure and memorable password by other means.
[1] As I've said in a few places, the actual dictionary size and number of words should be tweaked to make the security level appropriate for your needs, which will vary by application and grow over time.
So my problem is that it gives the impression to be very secure whereas it's only secure under some conditions. (You have to pick words uniformly among the list of words.) Just like old password...