it is definitely worth playing, but if you played 2 and 3 before it, it will be a little bit rage-inducing, the combat is much more difficult IMO because of the rougher shooter mechanics. 2 and 3 had really refined combat, in 1 it felt sluggish and blocky.
And yes it's worth playing imo. The shooting, flashy powers and controls I find to be better in ME3 of course, but ME1 is less linear in level design and more my speed in terms of just about everything else (loot, exploration, side-quests, stat distribution, etc.). I didn't care for ME2 much at all gameplay-wise.
Dialogue options and conversations are much better in ME1 as well.
Has open world exploration, huge interactive maps and that feeling that you're in a huge place with secrets to be discovered that's lacking in the other two games and most modern games in general. And the gameplay is fine, the people who hate on the first game wouldn't know a good game if it bit them in the ass
Mass Effect 1 gets better and better with each passing playthrough, as you discover more sidequests, more planets if you didn't grind, different dialogues when you do story missions in different orders, alternate ways to complete or obtain missions. IMO ME1 had the most replay value. Side quests compared to the others have different ways of solving them, and some actually have dialogue, so you can talk your way into making the threat stand down, provoke them, etc.
And I agree with Runt. People just love to focus on exaggerating ME1's problems. I mean yes, 2 and 3 had better gameplay, but it's not like 1's is unplayable or broken. The thing I liked about 1's was that enemies would actually switch weapons if you get close to them, like Krogan pulling out the shotgun.
Also, squadmates have an equal amount of powers as you do. If you're a Sentinel, then Kaidan who is also a sentinel, would have the exact same powers as you. If you're a class that doesn't specialize in combat, than those that do, like Ashley and Wrex, will have more HP than you. They would also deal the same amount as damage as you if not more, depending on what you give them. Squadmates are equal with Shepard in terms of customization, like armor, weapons, etc. In ME1, it feels like your squad is actually feels like a team, as opposed to 2 and 3 when it's just shepard doing all the damage, and your squad is just there for back up.
Snitsky's Condoms. If she get's pregnant, it's not your fault.
It's a lot more slower paced, the combat mechanics are more RPG like than cover firing (though that's there too, in a primordial form.) with a lot more options in terms of abilities and guns/armor. I really miss that and which they didn't simplify that so much, though in turn the controls are clunkier in the first game imo which is one thing I think they did improve upon in the sequels but it's not intolerable. You'll have to actually explore the surface of planets to get to where you need to go often, which I liked but others didn't but just be prepared for that.
It's worth playing ME1 if only because a lot of the default choices in 2 and 3 are terrible (I think intentionally so, to get you to play the first.)