MD similar to the games? Grantd, I haven't playd them myself but my understanding is that they are fairly different in gameplay, story and the setting of the 'in-game universe' as well. Colosseum/XD are far more similar to the main games if you view it that way, imo, or the Stadium games/PBR as well using the same mechanics.
And that said, I'd have to agree with Sydian and go with Colo/XD as my favourite spin-off series. Most enjoyable ones I've played thus far and it helps that I quite like double battles as well, given most of the gameplay is in that form as well.
Others I liked include Stadium, Snap and the pinball games.