Here is the setup: you are locked in a relatively small to medium sized, circular room with a little cover around the edges. The room leads into another tiny cubbyhole room, from which comes an opposing squad of enemies, one of which is significantly more powerful than you. They attack. The battlemaster(you did click that link and read up on it, right?) charges you while his minions run around the edges of the room to surround you. Now depending on your class, this can be an interesting encounter. If on the other hand, like me on my first playthough, you were an Infiltrator specializing in sniper rifles, prepare for a vicious assault on your sanity.
|It may not be a tiny room, but it is certainly too small to hope to use a sniper rifle in.|
But what if you're, I don't know... a Vanguard? Then this battle is easy: hit the group with AOE before they spread out, knock the battlemaster on his face with throw, blow him to pieces with close range shotgun, and mop up remaining geth. If you screw up, you might die. This is excruciatingly annoying because every single game in the series is easier as a Vanguard, and not just because of biotic charge. The majority of the each game takes place in close-medium range corridors with chest high walls and a bunch of enemies. It doesn't take place in giant spaces where you can pick off one or two enemies efficiently from a distance and then be done, which is what the Infiltrator is built for. All of this is merely a specific example of failing to take something very important into account when designing quests and encounters that all classes must complete.
An encounter that every character class must enter should be setup so that each class can use their skills and mechanical unbalances to somehow overcome the challenge. If you want an encounter like this one, leave a way for a long range player to get an overhead angle on this arena from a longer range. Just provide some way for each class to use their specializations to succeed. I'm not saying that every encounter needs to be equally easy for every class or that the proper squad shouldn't have to be chosen, I'm merely saying that throwing a situation at a player that they are not mechanically equipped to handle as a character(even only if they choose a specific few classes) does not engage them in any way and is counterproductive unless you're trying to make an artistic statement about how sometimes you just need good luck.
This reminded me of the boss fights in Deus EX: Human Revolution. I put all of my points into perception, silence, speed, cloaking, and close and long range non-lethal combat. The game encouraged this with XP baits right up until the boss fights where it would suddenly say "Okay, for no reason you shall now have to kill this boss who is invincible to melee and non-lethal weapons," and leave me to run and stay as away as possible while trying to pick their health away using the last lethal weapon I had picked up but hadn't removed from my inventory yet. Both of these are excellent examples of how you as a designer or level designer should take the game mechanics into account and think about what kinds of characters the player might bring into the fight.