Here's the bottom line:
-You will be amazed by the size and resolution of the screen as well as the quality of the graphics.
-You will be disappointed by the movies. You're probably expecting them to look and run perfectly, just by dragging and dropping them onto the GP32. If you want something that seamless, get a PocketPC. With GP32, making movies compatible with it is a long ordeal and they look decent, but not great when finished.
-You will obviously go straight for the SNES emulator, and be horribly disappointed that it doesn't run full speed. However, try to get over it, because GPEngine plays many fantastic games that aren't on SNES, with just as good (and often better) graphics. You'll have to actually play games you've never tried before (because you didn't own a TG-16) instead of the same old SNES games, but I think that's for the best.
-You'll be pleasantly surprised at how good Doom looks and runs.
-You'll annoy everyone on the messageboards by saying things like "GP32 should be able to emulate SNES since my Pentium 133Mhz used to do it just fine!" and "What about an N64 emulator" and "Why don't they make a Neo Geo emulator?"
-You'll expect homebrew games to be much better than they are. Remember, these are incomplete little demos put together by coders IN THEIR SPARE TIME. Don't expect epic, commercial quality RPGs or anything.
-You'll bug everyone about Astonisha Story R and why it's not English. Same goes with all the other commercial games.
-You'll bug us for GP32 roms. This is a no-no.
-You'll be amazed at how it can play games like Monkey Island and Day of the Tentacle.
In the end, you'll get over your unrealistic expectations of what this thing can do and realize it really is a neat little gadget. It's not magic, but it's not like you're spending 500 bucks on it, so be happy with what you get.
In a nutshell? Yeah it's worth it.