I haven't played any Personas myself but my gf has Persona 2: Eternal Punishment and then I bought her 3:FES for her bday and then 4 for Xmas. 2 looked pretty interesting but I'd never put any time into it. 3 is very good but seems a little out of place compared to the previous ones. Just seems to be missing a certain bizarre charm from 2. That's the best way I can describe it. Very great on its own, but feels like something is missing compared to 2. She hasn't began 4 yet as she hasn't even finished Journey. (last thing I saw was the decision regarding Ryuji. [Ryoji?])
If I saw this thread before, I would've asked if it was worth getting 4 now since she probably won't be finished with 3:FES for a couple of months or wait to see if there will be a 4:FES of somesort.
I'm actually disappointed that 4 looks to be exactly the same as 3 just with different settings/chars, but I guess there's no reason to fix what isn't broken. Looking forward to seeing a sequel on PS3/360 and seeing how they take it to the next level.
I hope that DS SMT comes to America by May. That'll be a good bday gift. If they ever put both Persona 2s on 1 UMD in US, I'll be pretty tempted to finally play a Persona. But it probably wouldn't be enough.