I would personally argue that games arent getting better, but more popular. A decade ago, there was an incredible amount of variation in titles across the board. Development cost lest money and the genres were less clearly established. Companies were willing to take alot more risks, and put out varied and quirky games that aimed to satisfy certain peoples inner geek, titles such as monkey island and Elite are good examples of this.
Now however, as gaming has become much more popular and mainstream than it once was, we find ourselves recieving increasing numbers of 'safe' titles. Sequels to popular franchises, generic space marine vs aliens / contempory modern day fps's. Most of the mainstream consoles are pushing mainstream games, and we find little innovation in such platforms anymore. Whilst nintendo seem to be able to push alot of innovative idea's and games across the market, especially with the DS, we find microsoft and sony adopting a very safe aproach when it comes to what they are releasing on their platforms.
Then we have to look at these mainstream games, and question if they are infact better than the same kind of games we used to play 5+ years ago. Now I understand the arguement of nostalgia clouding our judgement to some degree, but take away the increases in graphics in alot of games, and ask yourself if the changes in the way the game runs in comparison to previous versions or similar products are improvements, or downgrades. Are storys better than they used to be? Is the multiplayer more challenging and more demanding than it used to be, lengthening the experience and increasing the enjoyment. I'd argue no. Its a well known fact Epic toned down unreal tournament 3 because new players to the 2k series were dying too easily and thus putting the game down without actually trying to get good at it.
Alot of games are easy to pick up and play currently. Now I dont specifically see this as a problem, but it would be nice to find that some new games took the approach of wanting to be challenging, rather than easy to pickup and moderately easy to master. Its a clear known fact that FPS's have slown down, with the drop in popularity in games like Quake and UT, and their lack of compatibility with the consoles. Thank god for quake live.
RTS's are still finding their feet in the maintstream market, but I do believe, as someone said earlier, were going to see more and more console friendly CnC clones pumped out on the consoles, and as soon as someone nails the RTS formula down properly, probably lots of repetitive garbage. Its definately got that way with FPS's, and has been for some time.
As the gaming industry continues to grow, I expect we are going to find ourselves with alot of games we are content with, but not impressed with. Its only the rare gems of the year such as games like portal that are ever really going to stand out in any experienced gamers memory. Let us hope that as time goes on, the majority of new gamers will realise that the same types of games really are being made over and over, and that it is time for something a little more developed and innovative to come along. We have boundaries for a reason, so we can push them. Would I want Coca Cola to rerelease Cola every year with some flashy new packaging and a new name? No I wouldnt, So why should we view this practice as acceptable with our games?