There is a degree of variance from studio to studio, but generally speaking, the work load is related to the game dev cycle.
In my experience there are 3 phases of game dev. Pre-production, production and last few months before ship.
Pre-pro is about exploring ideas, trial and error with music and story, and developing systems/tools that make production more fruitful and efficient. Well managed studios will put an audio person on at this time. MANY do not. This us usually a normal work period as far as hours go.
Production is where most of the assets are created and put in the game. Usually this is split into a series of 4-6 week milestones. The beginning of each milestone is relatively normal. At the end of the milestone you can expect evenings and maybe weekends.
The last 'few' months of a project are long hours. I put 'few' in quotes because EVERY SINGLE title i have ever worked on (12 or so years in game audio) has slipped its deadline at least once, and that slippage usually happens at the end. it is very dependent on the studio/management of the project as to how this goes, but its always hairy.
Another thing about game audio dev is that there is no "audio Post" period unlike in film/tv, where audio is the only team working on the title. Very big changes occur up to the last minute that affect audio hugely (new areas of the game, new weapons or vehicles, big changes to art, new dialog/story elements....). This makes predicting your workload very difficult.
Personally i really like game audio, but the gratification is delayed. I know audio leads that have worked on the same project for almost 10 years before it ships (that is the extreme), but game dev cycles are rarely less than a year and are more often 18-36 months depending on the size of the title.
The above relates to in-house work