22 point buy is fine, but...
I noticed a strain in a point buy system between character concept and optimization. Personally, I don't like this strain. I think it goes against the design precepts of 4e to sacrifice mechanical viability for character concept. This became an issue when one of my players was running a human rogue with a 16 Dex and 13 Int, because he felt being "clever" required an above average Intelligence score. Power-wise, this put him roughly equivalent to a 17 point buy character, since those 5 points in Int did not make a single bit of difference mechanically. The only modification he derived was a +1 to two skills he was untrained in and would never use. Not everybody wants to fit an 8 into their character concept. (For the record, I do not require people to roleplay their dumpstats, but some players either can't or don't wish to ignore the numbers on their sheets.)
Since in 4e, essentially only 3 stats ever greatly matter, I allowed any stat up to
16,14,14,14,14,14
16,16,13,13,13,13
If you were a race that did not have a +2 in your prime stat you could use
18,14,12,12,12,12--
You can always choose a lower stat if you wish. This means your top 3 stats are equal to what you'd get in a 22 point buy, but your bottom 3 stats are whatever fits your character concept. (the off stat one is slightly higher).
This had a nice side effect...it made some feat qualifications a little easier to qualify for...things like light armor characters qualifying for light armor specialization, and great weapon fighters being able to qualify for heavy blade feats.