Most of the time, yes.
You look at the presentation first (music, menus, how menus fade-in/fade-out, etc.), then you look for depth in the gameplay. It can sometimes be hard to justify if the gameplay has depth when playing RPGs or strategy games because you don't get to see everything in the first five minutes (you can usually guess though), so I usually rely on presentation most of the time for these type of games.
Usually, when I don't find anything special about the gameplay, I put it in the mediocre game category already. Games like The Legend of Dragoon come in mind. I mean, there's simply no reason to level up your guys after you get all the combos (you realize that you can transform into dragoon form at a later point in the game, but it still doesn't add anything other than mastering the button presses at the right time). Battles are repetitive and pointless at this point. This doesn't mean that the rest, like story and music, are necessarily bad.
So, in other words, if the presentation is well done, the gameplay has a chance to have lots of depth to it which influences my first view of the game. I will say this though, I usually go through all my games and I can sometimes find little gems. Since it happened quite a few times before, I try not to "judge books by their covers" as much as possible! It's still obvious that some games are just bad though, and it can make sense with what I said above.
