Non - Rather than levels, have skill points based on what you use.
If your a gun-ho machine but leave lockpicks, terminals etc alone and plough through the game in an aggresive manner, it should reflect this, and vice-versa..
I disagree. The learn by doing system doesn't, imo, fit in Fallout at all. The game reflecting how you play should be handled through much higher skill effects (both good and bad) and more frugal skillpoint economy, so that if you decide to go Rambo, you really need to focus on the "Rambo skills", and similiarly with every playstyle.
I'm generally in favor of what Gabe posted, though I'd do it a bit differently:
1-50 skillpoints cost 1:1
51-75 cost 2:1
and 76-100 3:1
(this, as I think it'll be easier to make the skills worthwhile throughout the whole scope within a smaller range -- like, in Fallout 2, with the 300 skillcap, there was never any real need to raise the skills much, if at all, above 100)
And as said, much much higher impact from the skills. And a skillpoint system which considers the chosen difficulty (example: play on normal and there are no bonuses or hits, set the game easier and all the skills get a bonus, set it harder and they get a hit -- resulting in easier gamer getting to max out more skills and maybe even a bit faster, and the harder gamer having the opposite effect).
And more over, slower leveling (at least about 1.5-2 times slower than what it is in NV), and a level cap at 50 or so. A rough example:
Spoiler How it is now (first number is the level, the second XP needed to reach the level from previous point, the third is total amount of XP needed to reach that level):
Spoiler z=n+(y+150)
z=xp for next lvl
n=xp 'til prev lvl
y=previous xp raise
2 - 200 - 200
3 - 350 - 550
4 - 500 - 1,050
5 - 650 - 1,700
6 - 800 - 2,500
7 - 950 - 3,450
8 - 1100 - 4,550
9 - 1250 - 5,800
10 - 1400 - 7,200
11 - 1550 - 8,750
12 - 1700 - 10,450
13 - 1850 - 12,300
14 - 2000 - 14,300
15 - 2150 - 16,450
16 - 2300 - 18,750
17 - 2450 - 21,200
18 - 2600 - 23,800
19 - 2750 - 26,550
20 - 2900 - 29,450
21 - 3050 - 32,500
22 - 3200 - 35,700
23 - 3350 - 39,050
24 - 3500 - 42,550
25 - 3650 - 46,200
26 - 3800 - 50,000
27 - 3950 - 53,950
28 - 4100 - 58,050
29 - 4250 - 62,300
30 - 4400 - 66,700
How it should be (first number is the level, the second XP needed to reach the level from previous point, the third is total amount of XP needed to reach that level) for example:
Spoiler z=n+(y+200)
z=xp for next lvl
n=xp 'til prev lvl
y=previous xp raise
2 - 200 - 200
3 - 400 - 600
4 - 600 - 1,200
5 - 800 - 2,000
6 - 1000 - 3,000
7 - 1200 - 4,200
8 - 1400 - 5,600
9 - 1600 - 7,200
10 - 1800 - 9,000
11 - 2000 - 11,000
12 - 2200 - 13,200
13 - 2400 - 15,600
14 - 2600 - 18,200
15 - 2800 - 21,000
16 - 3000 - 24,000
17 - 3200 - 27,200
18 - 3400 - 30,600
19 - 3600 - 34,200
20 - 3800 - 38,000
21 - 4000 - 42,000
22 - 4200 - 46,200
23 - 4400 - 50,600
24 - 4600 - 55,200
25 - 4800 - 60,000
26 - 5000 - 65,000
27 - 5200 - 70,200
28 - 5400 - 75,400
29 - 5600 - 81,000
30 - 5800 - 86,800
31 - 6000 - 92,800
...and so on up to, say 50
The formula I made may not be correct, but the point remains. The speed of leveling - the gaps between levels - can be adjusted by the "constant" (is that the correct term?), meaning the number, in the formula.
And SPECIAL handled so that when 5 is the average, going below will have negative impact (and possibly postives too in some cases -- low intelligence character plus Torr in Fallout 2 come to mind as a good example) instead of merely lessing the bonuses that start from stat of 1 (and of course much higher impact from the stats, for all this to matter).
And perks every 3 levels, unless a trait changes it. They feel much better and more worthwhile when they are handled more sparingly.