Combat is a mixture of squad based action and cover-based FPS shooting. Cover plays a huge role which makes moving through areas very tactical.
Similar to Knights of the Old Republic, you are not in this alone. You will eventually pick up 6 different squad members and you will have 2 of them with you at all times. Their classes are varied (and slightly different from your own class options), so you can pick teammates to fill gaps in your own skill set in any way you prefer. Certain squad mates have unique dialog options when teamed with other squad mates which can really be a pleasant surprise. This also adds to the numerous variations in game play depending on how you choose to play the game.
Once you are in battle, you aim weapons and biotics like a first person shooter but your stats and gear affect how much damage you do or how accurately your shots land. The game does an excellent job of giving you control of where you are shooting while still rewarding you for advancing your abilities and level. You can also pause the game at any time to issue commands to your squad mates, help yourself aim (particularly handy for people who are not big on twitch gaming), or to plan out your own attacks, biotics, or tech abilities.
Enemy AI is not bad at all. Your foes will use cover, try to flank you, make effective use of their own strengths and abilities, and generally require that you think about your strategy. Combat is a lot of fun in this game and is never something that drags down the story or the pacing of the game.