MRI, could you give your thoughts of excellent level design and give your guidance?
Is it the same approach with level design when you're making isometric or first person view game?
Assuming you meant MRY...
I'm not a level designer, I'm not even much of a designer, so I'm probably not going to be able to give an interesting answer, but I'll try.
To begin with, I think if you abstract sufficiently, then, yes, isometric and first-person level design is the "same approach" -- but that abstraction is probably something like "make sure that there are multiple paths through a level, that there are portions that are harder to get to and provide some reward for reaching," etc. (Obviously, what
kind of game, like RPG vs. strategy vs. shooter, would change even the abstract level considerations. For example, symmetry and/or balance is irrelevant in a single-player map, but very important in some kinds of multiplayer maps.) I think multi-pathing, however, is true of every kind of game I can think of -- everything from F-Zero to Super Mario Bros. to Starcraft to Super Smash Brothers to Skyroads to Gauntlet to Fallout to Doom offers multiple different paths. The only exceptions I can think of are fighting games and space sims, which generally have empty levels. Even adventure games, which typically require the same checklist to be completed, offer you multiple ways to order the items on the list.
But once you're past that level of abstraction, I think the principles start to diverge along multiple axes. You can't have level design independently of ruleset. Very few isometric games have verticality, and of those few, not many do it well. So at a very basic level, you have to ask whether elevation matters, or even more basically, what the movement verbs are. Thus, the design rules for a a Freespace level, a Descent level, a Quake level, and a Doom level are all going to be very different because of how they engage with movement, even though nominally each is a first-person game in which you are moving and shooting enemies (throw Deus Ex and Alpha Protocol in if you want even more divergent examples). Another axis is "realism" -- sometimes maps are meant to evoke real(ish) spaces (Grand Theft Auto or Bloodlines or Ultima VII), and sometimes that kind of realism is not as important to the experience (PS:T or Super Mario World or Skyroads), so you don't worry as much about the "ecology" of a map and so forth. Another axis is "narrative" -- some games are more narratively inclined, and so you care more about designing levels in a way that feeds narrative to the player (typically through choke points with some narrative content), or thematic progression, or whatever. The stronger the narrative component, the more diminished (typically) the map's variety will be.
Also, there's a huge difference between levels where you go from start to end and then go to the next level and open(er) worlds. For example, it's a little strange to talk about Sigil as a "level" -- even though that is one way to describe it -- because it is doing something totally different from level 4-2 in Super Mario Worlds.
Anyway, at a high level of abstraction again, I think a really important thing is that levels, by default, need to inflict attrition on the player-character as he moves through it. The best case against this rule would be one-hit-kill but infinite-life platformers like, say, Super Meat Boy. But even those levels have a very basic form of attrition, namely a time limit. One considerable problem I have with a lot of RPGs is that the attrition is so trivial as to be non-existent -- the only resource being depleted is the
player's time. But you want to be draining ammo, HP, food, magic, whatever because the attrition gradient of the level is what shapes the player's choices on the game layer of the game. (There may also be a narrative layer on which the player is making choices, but if those aren't liked to an attrition gradient, then I don't really think we're talking about a game.)
Candidly, there aren't
that many games that I immediately think of as having good level design. Obviously Deus Ex and Thief, a great many platformers (Super Mario World, for example), Doom and Descent, there were some great levels in Gladiator (a DOS-era Gauntlet-ish game), I enjoyed Enemy Territory's maps. Meh, I'm sure if I thought about it longer I could come up with more.