Well it can go two ways.
If your DM does not have an instinctive knowledge of what tables to consult or (more importantly) when to stop with the complexity, it is an awful, grinding game that is frequently bogged down in life-or-death situations that require upwards of an hour (it really happened!) to resolve.
If your DM knows his stuff and (in my opinion) keeps to the more simple tables it is a good game, albeit one where you simply cannot plan ahead (one good/bad roll will utterly ruin you/give you a moment of awesome). If you want to capture the grit and chaos of real-life engagements then rolemaster is for you. And yes, I've played in a game where this happened.
At the moment, my 3.5E group is houseruling in this level of complexity, anyway, so there doesn't seem to be a great deal of penalty for going to a more complex system (the House rules packet grew to > 200 pages).
So I am happy if we can acheive the design goals of a system with complexity but fewer total rules to memorize.
But the point about the need for system mastery on the part of the DM is an exceedingly good one and worth putting some thought into.