Personally, I've never bothered with multiplayer co-op online games for handhelds. Hopefully Sony's online-play isn't comparable to nintendo's which is totally useless. My train-of-thought is more along the lines of: if your going to play a FPS game then you may as well play it online with PC/360/PS3. I guess what I'm trying to get at is: in my experience, all multi-player/co-op on handheld devices has been utterly terrible.
All-in-all, for a single player, like myself, who enjoys RPG games as well as homebrew capability, custom firmware is an awesome, must-have firmware extension. The PSP has become the most [hacked] handheld that I know of so far in that it has awesome cumulative library compatibility w/ a huge variety of emulation and homebrew applications plausible and it doesn't need a 3rd party accessory such as an Acekard2i or an iPlayer.
Everything considered, the only real downside to the PSP at the minute is the fact that E3 is 2 months away and knowing whether the new handhelds [let's face it, there will be new handhelds xD) will have backwards compatibility with PSP memory-stick pro duo's or photoflash CR-5400 / Micro SD.
Ultimately, the amount of content you have on your device is memory card dependent so it will be interesting to see whether or not new devices incorporate the feature with regard to whether their respective device will get hacked for homebrew capability. Personally, I think they'll utilize MicroSD/Pro Duo considering the flail that was the PSP-Go.