But this is just Mass Effect 2 right? Is there any sense buying it without having played the first game? Does the story continue onwards from the first?
Yes there is, but for a game so absolutely based on the story and characters it might chance the perception about the series for some people that never played it before. Playing the first game is not mandatory to enjoy the second, but it would be certainly a good idea for those who like ME2 and never played the first.
The first game has an even better story than the second, but the second is globally a better game.
I missed the Mako though. The new scan system to obtain Iridium, Paladium, and other metals is fine if you don't want to explore new planets. However, I liked the exploration aspect in ME1 and finding anomalies that way. Even so, the Mako was also flawed, so in Mass Effect 3 they will probably find a balanced, halfway solution between the exploration to find anomalies and the new scanning system.
In Mass Effect 2 they developed the new characters more than the story.
Mass Effect 1's story is much more epic. It's surprise after surprise. You also take very important decisions in many regards. Besides that there are people like Wrex, then things like letting the Rachni queen live or die -they are a pestilence and a killer race in the galaxy but if you kill her you cause Rachni's extinction-, the Protheans, the story of the Reapers, when you find the Prother needle, other Spectres like Nihlus, the Council, etc etc.
The final boss in ME1 was also tough and very epic, even playing in the easier difficulty levels. Saren was a great baddie and final boss.
I have to admit that the story in Mass Effect 1 is much more developed, maybe because the second part of the series suffers from the syndrome of the second parts of a trilogy, or whatever. The so called introduction, body (or climax) and ending thing. In the end, it's easier to tell the beginning of a tale, and an ending, than the body.
Mass Effect 2 is like the turning point of a narrative work, leading to its point of highest develop of the story in which the solution, I think, should be given. I expect the final outcome and denouement of the game to preserve the epicness of the first game, and maybe enhancing it. I kept playing the first game because, apart from the fact that it was something new and original with a great universe, the story had me totally hooked.
As a game, despite some simplifications, ME2 is a better game than 1. I missed the inventory system of the first game though. The inventory kind of sucked in ME1 because it only added a lot of hassle, but they should have changed it instead of getting rid of it completely.
The characters in ME2 are better, a helluva nice bunch of people with different personalities. Really good stuff.
Other than that, it's the most interesting retail game of X360, with overrated games like Halo. But this is normal in an industry where if you don't score certain games with a 10 the developers don't let you have access to some content like videos or pics, detracting your webpage -sigh-. But that's a different story.
Compared to Halo or Gears, in my opinion, Mass Effect is a Porsche and those are a Fiat Panda. Gears can be fun though, and Halo 1 and 2 were okay too.
Bioware are gods. And EA are godesses and gods too. In my opinion, it's the best gaming company that there is -not counting Nintendo since they only work for their consoles-.
As for your third question... yes, the story continues onwards from the first. It's a pity that taking into account the Blu-ray capacity to store information, they don't port ME1 too.
I don't know what their approach will be in order to allow PS3 users understanding the full story behind the game. There are walkthrough videos on Youtube, but it's not the same. Apart from that there is a nice, short video in ME2 demo featuring a quick, and well done, summary of the first game's story, but obviously it's quite limited.
The ME universe and story is quite fascinating and the strong point of the franchise. It's not the best or most complex adventure, not the best or most complex RPG, and an average shooter, but as a mix of genres they managed to make an very lowly flawed game, with a lot of great things to offer.
I applaud Bioware's imagination to create such a rich and complex universe, no pun intended. Apparently, there will be more details about ME2 PS3 version soon, so we will see what they come up with. I guess they will add all the DLC for free and perhaps some exclusive missions.