Yeah, Resogun was ported over by a different developer (Climax) and for some reason (not just graphics imo), just isn't that fun. However, Super Stardust Delta was actually made by Housemarque and is every bit as good as the PS3 version (if not better).
There are so many good games available to new owners, that it would take quite a while to list all the worthwhile ones. But I play a lot of indies on my Vita, that I probably wouldn't bother playing on a home console. What types of games do you like?
Of the bigger budget games, the ones that made the fewest compromises going portable, were Killzone Mercenary, LBP, Wipeout and Virtua Tennis 4 (I don't think LBP is native resolution, but it still looks fantastic). Even though you just got your Vita, hopefully you've been grabbing the free PS+ games since the beginning (specifically Uncharted and Gravity Rush). If you have, you probably don't need to buy a game for a good long while.