Much more enjoyable than part 1, the opening sequence alone is worth the price of admission. But it definitely has some serious flaws. There's literally no character development, except one guy who makes the mistake to announce that he'll retire next month to live with his girlfriend in Paris (You should never do that in an action movie!). The very simple, almost nonexistent plot (Track 'em, find 'em, kill 'em!) is just a means to send the Expendables from one…