Mass Effect 3 is the most disappointing experience I've had in gaming, made even more so because the talent and quality of the coding and game design is betrayed by shoddy and abysmal writing. If you play these games purely for the minute to minute combat experience, then by all means buy this game. If you have anything invested in the story and characters, then you might be best off skipping this installment and simply making up your own final chapter in your head.
The good + The very refined and polished combat of the second game but taken to a slightly higher level + Increased level cap of 60 + More choices in how to upgrade your powers + More bonus talents to learn from squad mates + Your choices from the previous games are frequently referenced, but not with the mass effect you've been led to believe in the marketing + Multiplayer is quite good due to the great combat engine
The bad - Far fewer squad mates - Less variety in single player due to fewer available squad mates - The main mechanic of the game is to increase a war readiness rating, but in reality it has absolutely no impact on the end chapters or actual endings, so this is a major lie to the player - The "thousands" of variables tracked on previous decisions in the older games have shallow impact. Specifically, they can help or hinder the war readiness rating, but again this rating doesn't turn out to matter. So, none of your other decisions mattered either other than your enjoyment of them at the time you played them out. - Multiplayer. Yes it plays well. However, every game is an 11 round co-op with the same "variable" objectives on the same loop. There are also only a handful of maps. It gets old really quickly. Also, you are rewarded with multiplayer credits to spend on multiplayer equipment packs. These contain random loot, and it gets tedious to keep buying them and getting the same thing even when you've maxed it out (they can stack up to a point). - The ending of the single player campaign. This is absolutely atrocious for many reasons but they can be boiled down to two things: -- One - the end game sequence is simply tedious. After a great build up, the take back earth event is itself entirely anti-climactic. The combat becomes tedious and ends up with a few "last stand" set pieces which have infinite monster closets until you hit the magic button to trigger the cut scene. Pretty crappy. It also does not lead to what you expect, such as the awesome climax of Mass Effect 1 where you were fighting on the outer hull of the Citadel. -- Two - Once the last stand is complete, you expect to continue on in an epic battle. Instead, you spend 30+ minutes walking so very very slowly around and being forced to endure minimally interactive dialog. Once this tedious sequence seems to be at an end, you instead endure another one. Finally, you are forced into the role of mute observer (a la Grand Theft Auto 3) where an awkward and obnoxious character (think the architect in the Matrix movies) shows up and forces you to make one of three decisions based on a demonstrably false pretense. The character's rationale can, with the right choices, be false on its face yet you are given no opportunity to reject his ideas. The ending cinematic is painfully short and light on detail; it is also almost identical regardless of choice. - The post ending - let's just say that if you watch the credits through they then make an obnoxious writing gaffe that should never be made - it is almost as bad as telling you that the whole thing was a dream. - The post-post-ending is that they tell you to buy more DLC
Why is the ending such a big deal, it's all about the journey, right? - No, actually it's not, at least when dealing with a story driven game. The fact is that Bioware promised "16 radically different endings" and they delivered 3 radically similar ones instead that have little to no bearing on your choices. Furthermore, I had characters that supposedly died in the end game that appeared in the post-game cinematic.
Finally, there seems to be only one logical conclusion from the basically identical endings: Bioware already has their next story arc planned out and they wanted to force everyone down the same path so that they could claim with a straight face that your ending was canonical. They'd have been better served to let us get the 16 radically different endings they promised, then when the next games came out they could've just said what was the canonical one without a negative impact on the original trilogy.
The bottom line - if I could get back my money I would; I won't buy any DLC and I won't preorder any of their games again. I'm also very unlikely to buy any additional Mass Effect games until their story arc is complete.
Bioware did a poll on their forums and ~90% of customers responded that they hated the ending. When you are an entertainment company with that many angry customers, then you should respond appropriately, not hide behind the aegis of "artistic integrity." When the answer to the age old question "Are you not entertained?" is a resounding "NO" then you are not on the right track.