I've been using a daily dose of 5g of creatine for several months to help with climbing. Maybe I'm a non-responder, or maybe the effects are too subtle, but I haven't noticed anything. Definitely nothing in terms of brain functions or what not.
It's cheap enough to continue to do it though, so I kind of keep at it.
I tried creatine out for a while. It definitely had an effect on me; previously I tended to tire out in my strength workout prior to really pulling the muscles and I tended not to have to be too careful about that. Creatine allowed me to workout longer without realizing it, to the point that I was in some pain for the next several days on those muscle groups, rather than "maybe sorta sore the next day for a bit".
Whoops.
With a bit more work I was able to tune myself to stop that, but it didn't buy me much.
In the meantime I noticed no cognitive effects strong enough to be noticeable without full-on Gwern-style careful testing. (My policy on that is that if the power of the result isn't big enough for me to notice in "normal life", I'm not that interested.)
I can believe that dedicated athletes can use it to good effect but I don't think I recommend it for casuals such as myself. I also definitely had to be extra-sure to drink more water than I felt like I needed or I would get dehydration headaches.
Have you tried creatine loading? Take 20 to 25g per day for a week, then take 5g/day for a month. Take a few weeks off and do it again. That's what I've done in the past when I was taking creatine for a recovery enhancer.
There was a research that concluded that after a month, there is no difference in creatine amount in blood if you've been loading or just taking 5g daily.
I've only ever heard of creatine loading as a way of getting an early kickstart for workouts. I didn't think it was even supposed to help in the 1+ month window, just get you better training results for a week or two up front.
It's cheap enough to continue to do it though, so I kind of keep at it.