To enjoy must of the fun of Dokodemo Issho, you'll need to have quite a grasp in the Japanese language.
The game starts you off by selecting the animal you'll want to befriend (Tama is the white cat on the package, but you can choose from several others). Once done, you'll begin to interact with Tama. Apparently, this cat loves to learn new words and interact with others, so he'll be more than happy to talk to you and discuss various things. He'll also ask you personal questions, such as your birthday, who you live with and so forth. The game has a real time clock, so it's defiantly a nice touch to the game.
The biggest draw to the game, however, is teaching Tama new words. You can teach it any word, and it can become a new thing in his dictionary (For example, "Hello" could be a threatening word). It's such a big thing in this game that you can add around a hundred words to the dictionary, and as Tama spreads the word about the new word, it'll soon pop up everywhere: On blimps, on billboards and so forth.
However, as I mentioned before, you need to have a strong grasp in Japanese in order to truly enjoy this game. This isn't one of those games where you don't need any japanese knowledge to play; You really do need it. Without it, you only get to enjoy half the fun.
Graphics are decent enough, and they don't try to push the power of the PSP that much. Load times aren't too fast, but then again, they aren't too slow either. Considering you don't get into loading that often, though, load times aren't a burden in this game.
Sound is quite quirky and cute, to say the least. Tama's steps generate a "squeak squeak" noise in a typical, cute creature tone infamous in most anime series. The music mixes well with the setting of this game too, and can be quite addicting (Think Animal Crossing's music).
With that said, the game is good, but unless you know japanese, this is one game that shouldn't be imported. It's a shame Sony never decided to bring their mascot game here in the states, but considering it's aim, I can understand why they would assume this game wouldn't sell.