The big question I have in my mind about opposed rolls (ignoring the time, etc, issues) is the double randomness it can create, and the tendency of negative effects to pile up on PCs. What I mean by this latter statement is that a PC, unlike an NPC or a monster, generally has much higher longevity in a game (indeed, often years) and thus negative effects can disproportionately affect them. I’ve often heard it explained mostly around critical fumbles: if you have a 5% chance of a fumble (and doing some damage to you in return, or some other nasty effect) then for the average monster who will be around for 5-8 rounds it’s not a big deal, but for a PC who’s around for years then those negative impacts will add up over time to reduce their effectiveness.
As a player, while I may cheer the time where I roll poorly to hit, and the defender rolls even more poorly, I’m not sure that would not be overshadowed more often by feeling I rolled great and keep missing because the monster rolled better or, even worse, I pull of an incredibly competent balance check, smiling as I walk across the tightrope, and the DM rolls high on the opposed check and I go plummeting to my doom.
If opposed rolls erode the feeling of being competent adventurers rather than bumbling young fighters who destroy trade federation ships through sheer luck (of doubly lucky dice rolls) then I do not want opposed rolls in the game. And I’m willing to see what it looks like in the playtest to see if that is how it feels or not.
peace,
Kannik