When the job is good, its great. When it is bad, it absolutely sucks.
For perspective, I work at the eastern side of Surejet. I've been here for 4 years and even if things turn awesome in an instant I'm still looking at 2+ years for an upgrade.
The good: The flying can be a lot of fun. You get to do a lot of things that you'll never get to do in GA. While not that exciting in the sim, your first cat II approach to mins will be an eye opener. You'll fly in some challenging situations that can really make you feel good after you work through them. You'll work with some great people. When nonreving works, its pretty spectacular. In theory, you'll have the ability to walk to any airport in the US and get on almost any airplane to anywhere. The first time you're strapped into a first/biz class seat to somewhere overseas, you'll be expecting someone to come bursting through the door at the last minute to accuse you of stealing. But instead, you're sipping on a glass of champagne as the door closes and the jetway pulls away. Almost everyone will find your job interesting and ask lots of questions. When you're finally able to gain the seniority, you can regularly work only half the days in the month. You'll get to interact with passengers and feel proud of yourself for getting them safely to be with their family, go to college, go to a job interview, etc. As you exit security, you'll see people from your flight run straight into the arms of loved ones and think "wow, I had something to do with that." Among other things.
The bad: The job can be greuling. You will be pressured to do a lot of things that you really shouldn't. You'll hear the ATIS say the winds are gusting to 50kts and know that the entire east coast is doing the same thing. You'll scare the pants off yourself. You'll fly some absolutely broken down pieces of crap and have to explain to the passengers why the gear won't be retracted for the flight, and its going to take a lot longer to get where you're going than it should. You'll work with some absolute s. You'll be subjected to their political, religious, whatever rants simply because they are in charge. You'll fly with a guy who refuses to kick the rudder out in a crosswind because "momentum will sort it out". You'll be stranded at different airports around the country when you are trying to get at home. You WILL miss important family gatherings (you might be single now and think that isn't a high priority...but odds are, at some point they will be). You'll be asked some absolutely stupid questions by people with zero manners "hey....where's gate 3C?" "Umm...that's your seat number." When you are junior, your company will own your ass. You will finish a trip on your birthday and be on your way out to see your wife in the parking lot because she has a weekend away planned, only to find out you were extended and are now out $300 that she spent to rent a cabin. This job is grueling, just as you finally feel recovered from your last trip its time to go back to work. After diverting to CAK instead of PIT you'll be told "now I'm going to miss my job interview and I'll stay unemployed, this is your fault!" even though the weather was the reason for the divert. At times you'll feel stuck at a company that has no future, but despite 4 years in the grind you're not "experienced" enough to move on somewhere.
If you're expecting someone to come on here and say "everyone who dislikes their job is full of crap, its great!" you are mistaken. Just like everything else, there's good things and there's bad. I promise you that when you "make it" it won't be anything at all like you pictured it. I thought I had a pretty realistic expectation for this industry, thanks to this site. Yet, I was still underwhelmed when I got here. Its not THAT bad all the time. Its more that maybe its not quite worth all that I put in to get here. But this is my trade, this is what I'm good at.