I quite like prestige mode, because it gives the game more longetivity. I play this game online way too much I admit (5d 18 hours and counting) but yesterday when I got Prestige level 5 I realised just how easy the game had become, in my 1st S&D match I got 1350 points and went from rank 1->6 in 1 game, and this was without any decent weapons as it was my 1st game I couldn't even "create a class", so I was stuck with the bog standard 3 weapons (thank god for the MP5), but the thrill of being able to do it again was brilliant especially when everyone around you has better equipment.
P.S. The 3 tips for ranking up quickly are as follows:-
1) Play HQ if your an average gamer, you should see a minimum of 250 points if your on a good side -> 700+ if your very good (games can take a while though). Play S&D if your really confident you can kill and not be killed. 50 points per kill is tempting, but this is what the best players in the game play so watch out.
2) Gun Challenges - don't mess around getting the digital camouflages or any crap like that. Simply complete the gun challenges for each weapon, usually in 3 stages. 25 kills = 100 points, 75 kills = 500 points, 150 kills = 1000 points (so that's 1600 points from each gun on average - there are exceptions to this such as the sniper/shotgun)
3) Other Challenges - There are some REALLY easy challenges to get some easy points, like blowing up 15 cars = 250 points. So does falling 30 feet or more to your death or falling 15 feet or more and not dying. also don't forget to lay prone and crouch, because this too helps challenges (just take a look in the boot camp for example).