Company: Microsoft
Date: 2014-12-28
Overall rating: 3/5
Employment status: former
Experience level: Senior

Great benefits, limited upward mobility and opportunity
Pros: As many have stated the benefits and pay at Microsoft are mostly without compare.  A healthy dose of 'work/life balance' and a solid set of benefits made this an attractive place to work for many new and mid-career people.  Recent changes to the review model is a huge step towards treating employees with the dignity and respect that they deserve.
Cons: Cons will vary by division, so my experiences may not be representative of all - or most - groups.
Within the the advertising groups ( i.e. in OSD or A&O) Microsoft is victim to a very subtle 'passive/aggressive' culture that seems somewhat pervasive of a lot of companies in the Seattle area (so, not just a MS phenomena).  Disagreements or direct confrontation is frowned upon, while 'back channel' negotiations and positioning drive influence.   If you prefer a culutre that is far more direct and vocal, Microsoft may not be a great environment or experience for you. 
Promotions and advancement can be very slow unless you have an acceptable 'alpha dog' personality and or othereise are a strong contributor and belong to high profile demographic groups.  If you don't fit these categories, make sure you get a level and salary you will be happy with when you start for at least two years or more as you will very likely not be considered for promotions until your second or third review (unless you stand out like a rock star).  Smaller companies reward and promote much quicker, so if you are used to or expect that, you may be disappointed.
While Microsoft makes much of its merit-based promotions/rewards system, its really difficult to believe it.  This is the problem of any large company where promotion and reward decisions are made further and further up the org hierarchy; so its just really difficult for all but the most signifciant (or narcisitic!) to get noticed.  This means that employees who consistently deliver good work but don't generate a lot of awareness can often be overlooked.
The lack of transparency around 'level's is one of the problems IMO:  Promotions are secretive and not acknowledged in most groups, which is kind of weird and doesn't lead to a lot of trust in a system if management is not willing to acknowledge who gets promoted and who does not.
The work you do may be exciting, but there is a 12 to 18 month cycle where the project/product you are working on will go from high profile to mundane or (as seen recently) a target for personnel reductions.  This leads to one of the solutions and problems at Microsoft in that you are going to have to change internal jobs frequently to stay relevant (e.g. 18 months to 2 years).  There is little value placed on consistent results generation; Microsoft wants rock stars who will generate internal enthusiasm and garner resources and rewards, which leads to a sort of self-fulfilling prophecy (until they ultimately flame out, see Xbox One launch!).