Thom and I are basically on the same wavelength about MechAssault, though I daresay I squeezed a little more enjoyment out of it than he did.
MechAssault may fit the bill as a simple shoot-'em-up, but from the perspective of being familiar with the original miniatures-and-stats Battletech game, it wasn't at all satisfying. Trimming and reworking the core concept, the developers left out most of what made the original appeal to me, like squad tactics and battle planning. After finishing MechAssault's single player campaign and digesting it for a while, I felt there were many missed opportunities for something beyond linear "point and shoot." Greater emphasis on the cerebral might have elevated the game towards a more filling experience. Unfortunately, it was not meant to be.
On the other hand, it's perfectly clear from the first few minutes of play that MechAssault has no intentions of replicating the source material, and that's actually OK. Despite any disappointment I may personally harbor, I like blowing stuff up as much as the next guy (possibly even more so) and the disc totally satisfies in that department. The sense of obliterating miniature environments is never fully dispelled, but it's still fun to trundle along and lay waste to every single thing in your path. Though not the deepest or most thought-provoking thing on consoles today, you can't deny the warm inner glow that comes from stomping infantry like ants and punting cars into the sides of buildings. Part of me yearned for more, but making things go boom definitely has its place.
Looking to the multiplayer side, Xbox Live gives the game legs well past the brief singleplayer experience, though few opportunities for strategy had been implemented at the time I went online (before the extra mechs and new mode downloads were available). The voice chat did add something, even if I found the standard deathmatch variations less than stellar. I have yet to try the new content additions, so hopefully some of the issues with the original load-out's slim pickings will have been addressed.
It seems to me that Thom's on the mark when he says that MechAssault has blurred its focus between the single- and multiplayer experiences. As someone who's not a fan of online play, I can't say I'm enthused the main game doesn't seem to have much invested in it. Although, much like Thom asserts, what the "main game" actually is, is up for debate. Online aside, if you're in the mood for a game where your higher brain functions can power down while reveling in some of the most impressive crumbling building and glass-shattering effects around, MechAssault is going to be your cup of tea.