Oh. That is definitely not the rulebook I'm looking at, and closer inspection puts the copyright date on the rulebook at 2006. I think I have the first ed. Were there flaws in 1st ed I should know about? Or am I better off just returning this and finding the current version?
Having played both, I'd say D1E and D2E are both flawed in about the same degree, but for different reasons. =P
Nothing that makes it unplayable, mind you. D1E and D2E are certainly different, but each has its strengths and weaknesses. I'd recommend keeping it for the time being, at least. Play it a couple times and see what you think; assuming of course that you actually have all the components you need. You can always resell on eBay later if you decide it's not for you.
I would say the biggest flaw, which is true in both editions of the game, is that it appears like a "D&D Lite" adventure game when it's actually a very intense tactical combat grinder. A lot of people buy into Descent as a replacement for D&D and are somewhat surprised at what they find. Like I said, that's true of both editions, though.
D1E takes longer to play since there are more bits to set up and the maps are generally bigger than D2E. But the biggest limitation you're probably going to come across is that it's OOP. Expansions will be harder to find, rules questions may take longer to be answered in online forums. That sort of thing.