I played half way through on a subpar computer and gave up.  Now with an updated computer I loaded ME1 and beat it in 2 days, 11hrs of game time.  I did Wrex and Garrus side quests and a few other planets, plus time getting lost in the citadel or with what to do next.  As I was approaching the ending I kept thinking, 'wow, this is going be epic.'  And then it ended....
 
I already purchased ME2 so I guess it did it's job, I was surprised though.

You're bloody quick then mate - took me 36 hours!
 
 I did get really into the fiction though - but you have to read that in the codex and stuff and be proactive about immersing yourself in the world.

I am on about 35 hours starting my 3rd playthrough.

My first character has clocked in just under 50 hours of of game play across 2 and a half campaigns.

Mass Effect really shines in the replay value. The game was designed for that very purpose with how you do all the quests and the variety of the choices you make.
 
However these things won't make too big of a difference until Mass Effect 2 comes out where your choices will make an impact on the story.

My first playthrough took 23 hours with all the sidequests completed and yeah I thought it was too damn short 
 
But I still loved the game and I'm on my fifth playthrough at the moment

The story is really short, yes. But the game isn't short because of the side missions. Sure it's no Bethesda length game, but that's really a good thing.
 
The ending does kinda happen suddenly though.

"15 to 20 hrs is about average for modern Bioware games. Both Kotor and Jade Empire were about the same lenth. Dragon Age: Origin is kind of the exception to the rule.  Personally I like the game lenth, It makes it easier to do multiple playthroughs. "

Yeah I played kotor and finished my first play through at around 26 if I remember right.

It REALLY depends on the optional stuff you do in terms of "short".
I bet you have 0 achievements on your Achievement page, as they all require you to invest time into side quests.

Technically a lot of RPGs are "short" if you don't do hardly any of the sidequests/exploring. Which, at least for me, is one of the main draws of playing those types of games in the first place.

Weird. My first play through in ME1 was under 14 hours as I recall. I did a few of the side quests but did not bother to check and "scan" most of the planets in the random systems. I really enjoyed it though, and at 15 bucks it was a steal.

My play-through time was just under 30 hours, which include doing all the side missions (except for the ones where you look for artifacts, minerals, etc. throughout the entire galaxy; I purposely skipped all of those), Bring Down the Sky DLC, and Pinnacle Station DLC.
 
While a lot of people found the side missions to be boring, I actually had fun with them since I enjoy the combat mechanics so much.  So 30 hours is not a bad length, especially when considering the directed path the game takes you through.

But that's like 59 hours, are you saying that's sort, or when you say 2 days, are you saying it took about 2 days with an average amount of play.

yeah ME1 main quest takes place on 3, 4 planets i forgot. reeeaaally short, like 5 hours short.

Why is this posted in Mass Effect 2's forum? Whatever, I found the game to be longer. But I usually am very slow paced in games like these.

59 hours is a short?

I had no idea that the game was so short.  I finally got around to purchasing a copy and was getting ready for a long game to get through.  That's kind of disappointing.

I'm on 50 hours.

Mass Effect is definitely short if you mostly just focus on the central quest in the game andignore the majority of the side missions you can run across. The other planet missions (which, lets face it, serve mainly for leveling purposes) do lengthen it somewhat though. I think all of my finishes are about 20+ hours, but I also spent a lot of time in conversations, reading Codex entries, that kind of thing. Also, as others have said, replaying is a must, as there are missions/conversations that only occur with certain backgrounds/psych types.

I finished my first playthrough in around 15 hours. I don't understand how you could go above 25, unless you like to take it really s   l   o   w. I also finished Dragon age with most of the sidequests done in around 36 hours, by the way.

ME2 is said to be 1.5X longer 
 
so its about normal length...maybe a little shorter?

My first time through the game I put about 40 something hours in. Yup. I talked to just about everyone, read just about everything. I got sucked into the fiction.

I'm playing Mass Effect 1 right now for my first time and am at Ilos now, which I got to pretty quickly.  I didn't do any side planets though... but I think I better do those now for a couple extra Achievements before ME2. 
 
On a side-note, I'm super impressed with Mass Effect 1, even though it's an older game.  Wish I would have gotten a chance to play it through multiple times, back-in-the day. 

" ME2 is said to be 1.5X longer  so its about normal length...maybe a little shorter? "

he didn't mean two days and eleven hours. He meant eleven hours spread out over two days.

It took me 35 hours my first playthrough. I explored everywhere possible and did everything that I could.

I was 22h to get through it and 35 on new game + because I did everything. Did you do any side stuff at all ?

That's a bummer as you missed out on a lot of side quests and as you do those the universe's story gets a little more fleshed out. I think I spent about 30-35 hours on my first play through.