I don't have anything much against them in principle, especially in a system (like D&D 5) where all characters can attempt to use all skills. That's cool. I also really like the simplicity of the proficiency bonus and the lack of "skill points" or whatever. What gets me, though, is the d20 system. I've ranted about this before on various occasions here and on google+.
My basic problem with it is that it introduces a very large random factor into things which, to me, don't seem that random. I'm totally cool with there being a large random element in combat (d20 + modifier vs AC) and with saving throws (d20 + modifier vs DC), but for skills it seems that the random element (d20) is way too significant. For example, the difference between the strongest person in the world (STR 20, +5 modifier) and an average person (STR 11, 0 modifier) is equivalent to only 25% of the random factor. I've always (since D&D 3) thought this seems weird, and WotC seem to disagree. Looks like it's time for a house rule then.
When I think about ability checks, what I really like is the semi-canonical, trad, "roll under your ability score on d20" system. Nice and simple. Rolling against a number on the character sheet. (Yeah, rolling low is better, how inconsistent... but whatever.) A couple of options:
Super Simple Roll-Under Skills
To make an ability check, simply roll d20 and compare it to the relevant ability score (as determined by the DM). Equal or under = success. A natural 1 always succeeds and a natural 20 always fails.
When making a check for a skill you're proficient with, add your proficiency bonus to your ability score.
Slightly More Complicated Roll-Under Skills
Sometimes you might want to give some kind of difficulty rating to an ability or skill check. You know... some chasms are wider than others, some walls slipperier than others, some locks more tricksy than others, etc. D&D 5 play material will no doubt be full of talk of "a DC 25 INT (History) check" and what-not. So it'd be nice to be able to use those difficulty ratings with a roll-under system. Here goes, DC to modifier:
- Very easy (DC 5): +2
- Easy (DC 10): +0
- Medium (DC 15): -1
- Hard (DC 20): -2
- Very hard (DC 25): -4
- Nearly impossible (DC 30): -8
I know that this completely changes the probabilities of success and failure. My argument is this: who cares? (Well, I gather that some people do indeed care about such mathematical aspects of the game, but I and no one I play with fall into that category.)
Roll-Under Saving Throws?
This approach could, of course, be applied directly to saving throws too, for the full old-school "roll against the number on your sheet" approach. Personally, I'm happy with luck (i.e. the d20 roll) being more of a deciding factor than raw ability when it comes to saving throws, so I probably wouldn't go down this route. Something to consider though.
They don't come up that often, in my experience, but I suppose I should also come up with a less random solution for opposed checks. That's easy: ability score + d6 (+ proficiency bonus, of applicable). Highest score wins.