Side missions are short bursts of action that see Shepard and his crew rescuing civilians, destroying enemy bases, fighting Reaper ground troops, and other miscellaneous objectives. They're much better than the last game; each one feels hand-crafted, and offers something unique, whether it's a fun set-piece, a new weapon, or some gorgeous scenery to stare at.
But the real meat is in the story. As Shepard struggles to recruit the main Citadel species to join his army, he finds himself fighting Reapers, visiting exotic planets, battling his personal demons, and locking horns with a rival group who seem intent on halting his progress. Going into detail about anything would spoil the surprise, but there are moments here that completely dwarf the scale and emotional impact of anything you've seen in previous games.
On a more mechanical level, combat has been vastly improved. With all the character interaction, story, exploration and other RPG elements, it's easy to forget that a lot of your time in Mass Effect is spent shooting monsters and crouching behind cover.
There's a greater distinction between enemy types this time, which makes firefights more tactical and interesting. Some enemies carry riot shields forcing you to flank them, or go for a headshot through a tiny slot on the front. Engineers drop turrets that can chew through your shields. Cannibals restore their health by eating the corpses of their fallen comrades.
It's an entertaining mix, and forces you to constantly rethink your strategy on the fly. The AI is more aggressive too; enemies will rush you and flush you out of cover with grenades. You can play it as a straight-up shooter - and there are plenty of weapons, from SMGs and pistols, to sniper rifles and flamethrowers - but you'd be missing out on the hugely entertaining tech and biotic powers, which are essentially sci-fi magic spells.
You can conjure up a miniature black hole that sucks enemies out of cover, and then blast them with a pulse of kinetic energy that sends their ragdoll corpses flying. Or you can overload their shields and stun them with an electric shock, then finish them off with a headshot. It's when you combine powers with regular gunplay that the combat really comes to life. If you play as the basic soldier class, the combat is far less engaging.
Shepard's more nimble, too. Tap X/A and a direction and you can roll away from enemies, or into cover. Whenever we found ourselves cornered by enemies, we'd tap triangle/Y to detonate our tech armour and stun them (we played as the Sentinel class, which is a mix of tech and biotic powers), then frantically roll away by tilting the stick back and tapping the roll button.
There's a new weapon mod system too. Each gun can have two upgrades plugged into it. Some are fairly basic, like an extended barrel to increase damage, or a scope for precise aiming, but there are others that add a new dynamic to the combat. Armour piercing is the most effective, as it allows you to shoot through cover.