I originally picked up this Xbox game for reasons other than playing it, but on giving it a try found it to be quite enjoyable.
What I've read about the game suggests that the bulk of its value resides in multiplayer action over Xbox Live, but never having tried it I can't say one way or the other. What I can say something about are the pros and cons of the single-player experience.
The presentation is solid, with everything looking, sounding, and shaking like it should. Even little details like the look of rain splashing off your mech are present and handled well. Controls are well-laid-out and responsive. Enemy mechs are tough and reasonably smart. They sure don't miss often. Level design is competent. Voice work is well-done. The overall experience is a fun one.
Pen-and-paper Battletech purists will probably find fault with the lack of mech customization options, but I found that the limited selection meant getting back into combat quicker. Some explanation of the finer points of mech vs. mech combat would have been welcome. The lack of checkpoints is frustrating; who wants to fight through an entire mission's worth of little guys a second time when the end-of-mission boss smacks the payer down in just a few hits?
Summary: Fun game, needs in-mission checkpoints.