+1 for PSP here, a few of it's virtures:
Great modding/homebrew community. I use it, in addition to gaming, as a comic book reader while in bed for comics scan files, an instant messenging device (so I don't have to spend money using my phone's costly MSN client), a Skype phone (requires special headset) for my long distance calls, and more :> I also use it to soothe me to sleep with the internet radio functions built in. Emulation side you have everything from the earliest game consoles and PCs up to PS1 and N64 fully emulated. Especially digging the GBA Emulator as it lets me play Mother 3 translation on the go
Games wise there's plenty if you're willing to look around a bit. I personally highly recommend:
God of War: Chains of Olympus (simple, awesome beat em up very similar to the PS2 games in the series)
Lumines (Addictive musical puzzle goodness)
FFT: The Lion Wars (beautified, re-translated to REAL english and with added art and animation to make things less boring remake of FF Tactics)
Jeanne D'Arc (a unique and awesome strategy RPG)
Disgaea (direct port of the PS2 game, voice acting and all included plus new bonus modes thrown in)
Patapon (an indescribably fun game that can only be described as a Rhythm game slash Real Time Strategy game)
Monster Hunter series can be great fun especially online, killing wild beasts and scavenging the corpses for supplies!
Star Ocean 1 and (soon) 2 have some excellent remakes on PSP
Perhaps of most interest to DF fans is Dungeon Maker, which has a combination of hack-and-slash random dungeon crawl while adding on rooms to attract more and better monsters, which has a lot of depth.
Ultimately it's your taste in games that matters most.
http://www.metacritic.com/games/psp/scores/http://www.metacritic.com/games/ds/scores/have some fairly complete lists
