Do you like apples or oranges? They both look good, taste good and provide different nutrients. What's that got to do with gaming? Most roleplaying games are based off of one of two systems: level based or skill based. Both have good and bad points, both have defenders and detractors. But which is better?
In skill based games, you usually build your character based off the skills that you choose. You make the decision on what he is good at and how good he is at it. This is very appealing because you can get a very broad based character with a wide array of talents, making him extremely useful in almost any situation. You may take so many skills that you only have a few points to divvy between them, but thats better than being useless in a particular situation or trying to make an "unskilled" roll. Later on in the game, you can even add more skills or more points to the skills you already have. Nothing like being 100% skillful in firearms right? In my opinion though, this can lead to a bit of min-maxing, aka munchkinism or power gaming. Any point based system like this has the potential of letting players stuff everything into one stat or skill at the expense of everything else. This makes them very impressive in one thing, but has a tendency to skew the challenges in the adventures they face. Most systems (and GM's, hopefully) have limitations and restrictions in place to compensate for this, but not always.
Level based games introduce the slightly unrealistic aspect of a "power level" or rank into roleplaying. A character starts off at level one as a newbie, greenhorn or generally inexperienced person. He then accumulates skill and knowledge as he adventures and progresses rather evenly overall, usually with a focus on a specific ability. Most level based games also include a "class" or profession that helps to define the character. Your level in the game shows where you rank amongst others of your same profession. Advancement in your chosen class does slow down as you achieve higher levels, and you dont have much choice as to how to improve your character when he does. You are stuck with whatever class (and its correlating abilities) you initially chose, though most games of this type give you plenty of room to expand within that class.
I have played both types of systems and seen the best and worst of both. Skill based games like GURPS, 7th Sea and Twilight 2000 are loads of fun, but for me will always lack something. Being an old school gamer, and being raised on D&D, I prefer level based games, if only for the defining aspect that classes give to ones character. It is of course a matter of opinion and taste, but it is also a matter of setting. This is why I believe that one generic system (like D20) is not appropriate for all genres. To me, skill based systems work better in technical campaigns, like modern or scifi, while levels work better with the more fantastical games, such as fantasy or superhero. No one way is right, and of course some games out there actually try to blend the two systems, some better than others. But for me, I will always think it more impressive to say "Im a 20th level Master Thief" than to say "my guy can pick pockets at 99%". See the difference?
