OOOuh, I still have the GBA one
I loved it and hated it at he same time. I really liked the story actually (I found it kind of cool to be better then everybody else at fighting robots :3), and I also liked the designs of the robots. I also kinda liked the evolving process of your robopons: you can evolve them if you wish, and later, they COULD be better then the first version of your robopon, but it comes with a heavy side-effect: it keeps a third of it's level and half of it's stats, which can be harsh if you decided to evolve your robopon before a boss :I
But that's also the thing I disliked about the game. It was long to level up your robopons at the end of the game, especially since the battle places were not made... correctly. For instance, if I take Pokemon, you got all the different routes with pokemons changing 1-2 levels when you advance in the game. In Robopon though, between 2 different places in the story, some robopons have a 7-8 level difference, which can be hard to level up. Hard to explain, but you probably get what I mean.
And other thing I noticed was an annoying sound bug. You know the old games had sound boards, right? Like, 8 row of bars for the sounds? And each time there's a sound, some bars will go up, etc. Well, in Robopon, if you were battling, the music would take a lot of those bars. But then, if you make a big attack sound that took, like, 3-4 bars, the some instruments in the music would stop playing for 4 seconds. I know it sounds retarded, but man did I hate not being able to listen to the music correctly!
And finally, the thing I hated the most: the loading screen when you start the game! It lasts 30 seconds each time you open it, just because the game shows the logos of the companies that made the game. That wouldn't be bad, BUT, to make robopons, you gotta put 2 batteries together, right? Well, if you make a bad combination, you get the weakest robopon in the game (Imagine a sperm with a light-bulb as a head and a wire as a tail). And sometime, you didn't WANT to lose those batteries, so what you would do is save the game before making a robot, close it if you got the bad combination, watch the loading screen for 20 seconds and try again 10 times before actually getting a good robopon combination.
Ok, long texts for angry comments, but I still liked the game anyway.... except that robopon, I always hated it.