[Kereth]

Well, here's the deal. RetroMUD is not a pk MUD, but we have PvP available, in the form of wars (everyone vs. everyone events) and capture the flag arenas (anything goes). The latter allows a great deal of team PvP and is optional for anybody who wants to participate and can be run at any time. Let's look at how it compares to your specifications:

-Coordination of roles/classes:
RetroMUD has 17 or so starting guilds, with over 50 or so secondary guilds and hundreds of tertiary guilds, combined with 60 plus races, all of them unique. This means every character in the match has unique tactical abilities, a unique stat set, and a diverse range of skills and spells that allow them to play a separate role in the arena combat.
-Interrupts
Most melee classes learn how to stun with normal melee attacks, and plenty of spells have interrupting side effects, such as holds, paralysis, blinds, knockdowns, poison, stat reduction, hallucinations and so forth. Additionally, a number of attack skills, particularly those found in the Hand guild, can give additional effects, such as scars, bleeding, etc, on top of those effects listed above.
-Ranged attacks/idea of a "battle line"
During a party, which can be formed during ctf as in normal play, players tend to take one of two roles, either front or mid row, meaning that characters with more defense and hp stand in front and take the brunt of attacks while others hang out behind them, launching whatever attacks they please at range, whether spells, polearms, whips, bows, crossbows, thundersticks, thrown weapons, slings, specialized attack skills, etc.
-Good maps
There are currently three basic arenas in game, each on a different world, with others planned and coming soon.
Wysoom Arena:
A raised, triangular path over water. Players without flight (whether from racial abilities, equipment, or spells) follow the paths between various points or swim through the water below, which those who can fly move freely through the air above. At the end of each point in the triangle is a base (flag base, red base, blue base). Each base is equipped with a spy glass to check on who is hiding at the other bases, as well as a trebuchet, to launched periodic volleys of burning rocks at the people at the other bases. Players may take advantage of every ability at their disposal, whether stealth, teleportation, summonable walls, summonable creatures, or whatever else, even down to the old fashioned "big spells to blow you up" or "arr and head smacking" strategies.
Raji Arena:
Flight is mandatory here (although fortunately easy to get) as Raji is the air planet. Floating islands in a three dimensional arena bare the different bases, as well as boulders which can be kicked around and even knocked at other players. Shrines of Gaia provide temporary elemental protection to those who choose to pray at them, and there is even a shrine that grants a powerful, 2-handed sword to whomever requests it, although the sword is dispelled every time the player is forced to respawn, and only a limited number appear each match. Constant air-to-air combat makes for a whole new dimension of gameplay in an arena designed for particularly large groups.
Crypt Arena:
The planet of earth's arena is completely underground. Narrow tunnels, lava pools, sulfuric gas clouds and sudden dropoffs are just the beginning of the trouble found here. There are pickaxes available, in limited supply, that allow players to sabotage tunnels to collapse on people passing through, and shrines give blessings to those who find and pray at them during matches, such as the shrine of eros, which grants awesome temporary power and protection at the cost of permanently changing the character's gender, or the shrine of mars, which hands out grenades!
-Mounts
I'm going to be frank with you on this one. We have mounts, yes, but nobody usually bothers using them during capture the flag matches. There isn't a huge bonus from speed, just energy used to travel, and those wanting to get from point a to b faster will generally use teleportation, flight, or just run fast on their own.

Now, leveling. Skill in the capture the flag arenas counts for a lot. Player skill, that is, but it only goes so far, so anybody wishing to get that extra edge from just plain having a more powerful character will need to level up. A team of level 20 characters can take out a level 100 character in a heartbeat, but they won't be able to do much against a full team of level 100 characters. Aside from fighting a little dirty, of course, but that's expected ^^ Still, the pvp experience is awesome and worth the leveling, if that's what you're into.

Hope you see something you like, at any rate!
-Kereth