This is truly a memorable level - for 2 reasons - firstly, it is superbly arranged with a variety of different types of action that is very nicely sequenced and, secondly, there is no pattern buffer, so the player will likely play it again and again. In that sense it is truly unforgettable. So was Pfhoraphobia, and I think that Bungie was wise to not do that to us again. And it was a good decision for the M1A1 folks to include a secret PB in their port of M1 - a secret first reported to this forum by yours truly, BTW. Unfortunately, Trojan has not one but 2 levels that lack a PB, and that's a bit much. I consider this to be a true flaw in what would otherwise be an outstanding level.
Putting the PB issue aside, Grenades is a remarkable level. It is deceptively simple, and yet highly complex. It evolves in stages, from the opening room where there is a substantial welcoming party, to the maze that follows, to the sequence of rooms leading to a large pit that requires an entirely different strategy, to a winding corridor that cuts you off from access to shield rechargers for quite some time, to the boxy corridors with enemies coming at you from unexpected directions, to the exit that is somewhat hard to find, to the "donut-shaped" room with lots of tanks and, finally, to the room with the wires that must be smashed and the ensuing ambush that follows. All of these are well executed and the story is solid - smashing those wires leads to a reactor core breach that will forever silence the GenCopr assault. Unfortunately, the risk of dying is high at every one of these stages and particularly at the end, when the player will likely have little if any shield strength left. I lost track of how many times it took me to get through this level the first time I played, but I do recall that it took 3 attempts once I reached the final room. Three attempts of playing all the way through before I finally made it back to the beginning to be teleported out. This time was a little better - I was very cautious and I knew where all the enemies were - I made it through on my second try.
All-in-all an outstanding level, but an exasperating one. In a few days we'll discuss a much less well-constructed level - Electric.