Ok, first off, I'm going to treat the two story lines like separate games. 

The Lost and the Damned was the first one I played. In all honesty, I wanted to get through it first because I wanted save Gay Tony for later.

This story has a lot less humor that is trademark in GTA. Everything is more serious and it has a very dark tone. Your club president, Billy Grey, has just come back from rehab (I'm pretty sure) and despite what he says, he's crazier than ever. Your character Johnny Klebitz took his position while he was gone and made attempts to settle disputes with other gangs. When Billy takes the reigns back, he blatantly breaks a truce with a rival gang that undoubtedly starts up a dump truck load of trouble.

One of my favorite parts of this game is the sense of brotherhood that you and your club members share. A cool feature is that you ride as a pack on the way to missions. While on missions, they even fight and can get you out of a tight squeeze. Since you won't be driving cars (you are in a motorcycle club) very much, you won't have to worry about not having space in your vehicle for your brothers. 

The game itself is long enough to justify the $20 price point (or $40 if you're buying the double dlc pack) and well enough fun. My only real complaint I guess is the same from GTA IV: the movement is still wonky and driving can be a pain sometimes. Don't be surprised also if you riddle some guy with an unrealistic amount of lead and he gets right back up. The supposedly fixed aiming system still kinda sucks.

The main story took me a couple of days to complete. It's close to around ten hours I think. All in all, I give The Lost and the Damned a 9.

The Ballad of Gay Tony was really why I wanted this game. From what I've played, there is still the satiric humor and outrageous characters. The main point of this story is very obvious: having fun. Base jumping is a welcome addition. Once you finish all the base jumping missions you even unlock a parachute in your safehouse to use whenever you want.

This story has you, Luis Lopez, as Tony Prince's business partner. Your club business has tanked and half of Liberty City wants you both dead. The majority of the mission are ridiculous and far fetched which only make it more fun. While working for Yusuf you will: steal a military chopper, steal a subway train, and parachute off the biggest building in Liberty City. Outrageous.

Between all your exploits you can work at one of Tony's clubs and monitor what goes on. It's actually quite fun. While not on duty, you can get down on the dance floor, drink shots, and take part in a drinking game. To add to the glitzy and elitist environment, there are some new cars. Some which include a gold plated Bentley look alike. Oh, and a gold plated helicopter... Hehe.

I have yet to complete the story thanks to a rather difficult mission I'm stuck on. But, I'd say that the story is probably around the same length as TLaD. Overall, I give BoGT a 9.25. In my opinion, I found it to be more fun than TLaD.

Both of these games tie into the original GTA storyline in subtle ways without trying too hard. It works pretty well. My only complaints in BoGT are the same as those in TLaD. Both are great standalone games that are worth the price and will get a lot of play.