There are a lot of fantasy MMO games avaible, there are only a few that include mecha and even less are free. Time to have a look at Exteel.
Exteel is a MMOFPS, or rather third-person shooter, as you can't switch into first-person view at all. Brightly coloured and futuristic, it supports up to sixteen players at a time within an overall MMO framework that includes customisable mechanaughts and special skills. Melee, ranged and AoE combat are all effective, but it lacks the twitch-response you find in dedicated FPS games.