Back when this series was an RPG.
So, I probably hold a minority opinion, but I find this game to be the best of this entire series.
Sure, it definitely has its flaws, and I am not defending those. Compared to what came after though, there is just so much more game here.
It's primarily a loot game - think Diablo but a third person shooter. It is much more linear than Diablo, however. But as with any loot game comes inventory management, which is where some players get overwhelmed. Let me simplify it for you: when scrolling through the weapons or armors you want to equip, if two or more of the attributes are yellow when compared to your equipped item, equip that new item. Done. Turn the rest to omnigel.
But when you aren't fiddling around with the inventory, you can shoot some things up with the guns. The gunplay in this game is satisfying for what it is. It is a tad on the clunky side, but I do like the rechargeable ammo mechanic. It gets really goofy later on when you get High Explosive Rounds. It's hilarious to just watch enemies get blasted into the air from a shotgun blast.
Which brings up another fun aspect to this game - gear customization. You can equip certain upgrades to your weapons and armor to assist during combat. Some make your guns have less cool down on recharge, some make your shields recharge super fast, some make your guns fire freezing, fire, or disintegrating rounds, some make your health super buffed, etc. There's a lot of customization and builds you can try that can compliment the class you choose.
Speaking of classes, there's really only one class to play: Soldier. Why? Because Solider is the only class that allows proper use of all weapons. Other classes try to compensate for this by having different biotic powers. While the game gives you the illusion of playing with these cool biotic powers... you're better off just using guns. The biotic powers in this game aren't fun to use as your upgraded weapons can do pretty much the same effects. Want to Stasis someone? Just pop on some Cryo rounds and blast away. Or just have one of your squadmates do it. The biotic powers do each have their own independent cooldown, so that's nice at the very least. They're there for experimentation if nothing else.
Speaking of negatives, there is the Mako driving segments. As others have highlighted, these can be a drag. A lot of the planets you land on will require you to drive this clunky brick through some odd landscapes that the Mako isn't really built to traverse. You'll find yourself Skyrimming up a mountain a few times.
If the Mako was more of a hovercraft and less of a rover, these segments would be more bearable. If would also help if there was more on the planets to actually explore.
People also like to pick on the Elevator loading screens in this game... I don't really mind them. They offer a moment of rest in between exploration or combat segments. Can some of them be a bit long? Eh. I guess. I never stood in an elevator and thought "Jesus! This is way too slow!" Maybe it was big problem back in 2007, but I don't know - I remember playing this game back then and not having an issue with it.
I also like for every enemy you kill, every objective you complete, you get XP. Really feels like your character is progressing the more you do. The leveling system is also pretty nice and decently balanced with each skill point you put in. I wouldn't say it is hard, but it does suffer from the common video gamey issue where if you play on higher difficulties, the more tanky enemies become. A lot of fights on Insanity are just wars of attrition and can make the combat really boring.
I hold the opinion that due to the Mass Effect series being more narrative focused, they honestly should not even have a difficulty select. There isn't Devil May Cry levels of depth here. It's shoot enemies, get XP, talk to person, complete quest, level up. Nothing bigger or greater.
With this series being narrative heavy, the one here is a solid set up: big evil thing coming to destroy all life in galaxy, and you need to stop it. It's simplistic, but it is engaging with how you can choose certain scenarios to play out. Characters can die. Friendships can be ruined. Monumental events can be decided by you. It's just a shame the sequels didn't really do a good job of using these decisions.
Many people praise the characters in this game and I will say there is a lot to love there. Garrus is always great as is Wrex. Tali is an enjoyable crewmate as well. Everything is well voice acted and it's mostly enjoyable to just listen to characters speak with each other. The arguments they have, the choices you can make - it's charming and endearing. You actually feel for what's going on.
This is an all around good RPG. It has its goofy quirks, but you could do so much worse (like turning the sequels into boring cover-based shooters that derail the story into stupidity and fan-fiction cringe fests).
I don't know what BioWare has planned for the future of Mass Effect, but I doubt it will ever get back to its heights here. Especially with most of the devs no longer being at BioWare anymore.
If you want a classic and goofy RPG to play in your spare time, try this game out. If this game is too arcadey for you and you desire a more modern/popular/trendy experience, the sequels might be more for ya, but don't expect a lot of narrative significance there. The second game might as well be a spin off with ass-pulled relevance to the main plot here.
You might be interested in picking up the Legacy Collection they produced a few years ago - it has some QoL enhancements to this game and the modding scene also helps a lot too.
