FO3 is an interesting example of a game with a low level cap -- interesting because it's not terribly hard to maximize a character in FO3 to get the highest stats in all areas.
My cry against FO3 is probably that the perks fall largely into the categories of either useless or essential, and so most characters I build have the same stuff. Maybe there's a small category of neutral perks that you can take to specialize your character, but it's still the same character. Just this character gets help from a mysterious stranger, and this character gets help from animals... Etc. I woulda liked to see more perks in the essential category, that would make me think hard and make sacrifices... but I digress.
The advantage to a high cap and NOT needing to specialize is that the system becomes more noob friendly. When you have to carefully manage your character and specialize from level one, then first time players often hit endgame with some mediocre character that doesn't do anyone one thing particularly well.
The advantage to having a low level cap and needing to specialize is that the game has greater replay value. If you can make one character that can do anything, then you're driven to continue playing till you max your character, at which point you may safely shelf your game. On the flip side, if you specialize your character each time you play through, then you are encouraged to replay the game with different character builds for different experiences.
A note: I like fast leveling systems in low-cap games. If the point is to make a really strong character with one particular strength, then you want to be able to reach that point. If I only have 20 levels to build my ninja-sniper-alchemist build in game X, then I damn well want to hit that 20 mark so I can finish my build and proceed to kick ass with it. Conversely, when your level cap is 80, 99, etc, then the game is already dragging out the leveling process for you and making you grind. Here, the hardcore can enjoy their grind (for whatever reason) and the rest of us can safely ignore the grind if we want to.
My preference: The low cap. 20-30 levels, where each level is important and meaningful, but also on a fairly fast leveling system. I don't like gaming to be a second job for me, I want to sit down and accomplish something in an hour of play. When I need to grind for 4 hours to get from level 18-19, then I'm not going to play the game anymore. Unless the grind is fun, like COD or something. But then, I don't find grinding prestige in COD to be grinding at all.
/2cents