I liked the idea of gun renting. It's kind of like Black Ops (hush friends) where you buy what you LIKE/ACTUALLY USE first instead of unlocking stuff that you won't and waiting- only In Combat Arms it was harder to earn cash.
Now obviously the bad thing about it- they need money somehow. You miss out on like 80% of the items if you do not pay with real money, then you'd end up paying $5 to rent a virtual firearm for like 3 days.
I'd like if some more games had a renting system like that as well, only a lot more balanced and didn't take you a year to actually purchase it permanently.