Median XL is a mod for Diablo 2: Lord of Destruction. It changes many features of the original game - basically, it revamps nearly everything. The following is a rundown of the more visible changes in the game.
Class changes and improvements
Each character class now gains life, mana, and stamina at different rates. Plus, the maximum character level is now 120. Also, who remembers the bug in the original game where your entire defence stat was ignored when you run? Pretty bad, right? The bug hasn't been fixed, but this problem has been gotten around simply by increased walk speed.
Entirely new skill trees
The mod features all-new skills for every class - every single skill and skill tree has been completely overhauled. Each class now has 25 main skills, 3 uberskills, and 2 challenge reward skills. Rest assured, the skills have been playtested extensively - no more 75% useless skill trees and everyone from class X abusing skill Y. Also, spell damage is now affected by energy ("energy synergy").
Blocking and Energy Factor
In the classic game, max block (75%) was ridiculously easy to attain, while defence was hardly worth investing in (exarcebated by the running defence bug). In the mod, defence now matters, and block% on items has been greatly toned down - but you can still achieve good blocking by pumping dex heavily. Energy factor is a bonus multiplier that boosts spell damage the more energy you have.
Improved Casting Speed
Caster characters (druids, necromancers, sorceresses) cast their spells faster when using staves.
Monsters have been improved a lot. They are more aggressive and dangerous compared to the original game's monsters. Many of them have had extensive modifications to their appearances, animation, statistics, and skills. You want a challenge, and Median XL delivers!
Elite and Heroic monsters
These are special monster spawns that feature enhanced versions of the monsters they are based on. Naturally, they give you better rewards for slaying them.
Veteran players no longer need stand around bored doing endless boss runs. On top of the 25 new superunique encounters and 21 special uberbosses, there are now special challenges for experienced players.
New base items
The items in the game have been improved upon - you will see far less useless stuff. Additionally, item stats have been rebalanced and reworked into six different quality tiers, each with better stats than the last. There are also special items which are even stronger than these. Finally, many animations have been speed-tweaked to encourage unusual weapons, so that not everyone from class X feels forced to use weapon type Y.
Sacred items are more powerful than the regular 6-tier quality items, but are hard to find and have high requirements. They cannot be gambled. They are also the only types of items which can be crafted, turned into honorific items, or be part of an item set. Sacred items also have their own uniques.
New set and unique items
The mod features all-new special items, with 470+ uniques and 28 new sets. Unique items may drop anywhere in the game, whereas set items have been revamped completely - they are all sacred-type (and thus cannot be gambled) and considered to be equipment for high level characters only. As such, set items only spawn in the special level 121 areas.
Sockets are much more plentiful. The socket count of an item is usually equal to the number of slots the item takes up, although lower tier quality items have a lower max socket count. Gloves, belts, and boots may also have sockets. All tiered and sacred items have a 25%-50% chance to spawn with a random number of sockets. Uniques, sets, crafted, and honorific items spawn with max sockets.
Enhanced affix pool
Tired of itty-bitty +1 hp kind of bonuses? Median XL features an improved affix pool, which results in stronger and better items. There are even item-specific skills as well as percentage-based bonuses, making magic and rare items a more useful and viable option for all characters.
New gems and runes
There are now more base gem types, and they have all been improved. Ditto for runes. The runeword list has been revamped entirely - the list stands at 490 runewords, currently - and there now exists gemwords. Gemwords are an affordable low level option for characters who are looking for a more specific bonus, such as a particular resistance. Everything is useful now!
Rebalanced drop rates
What good is an item if you will never see it in your lifetime? Drop rates have been fixed so that you may actually see a Zod rune now, among other things.
New Horadric Cube recipes
There are far many more uses for the Horadric Cube than ever. You can upgrade items, add enchantments, strip all enchantments, drill sockets, remove socketed items, and craft new items, just to mention a few of the uses. Also, the Horadric Cube is a necessary component in completing the various high level challenges in the game - make sure you bring your cube along, and take care that isn't filled with clutter!
A new type of requirement is now required for pulling off higher-tier recipes: Crafting Points. Crafting Points are available as affixes on equipment, and you must be wearing them at the time of attempting a recipe which has a crafting point requirement. So don't be too quick to junk that equipment with crafting points on it, you may need it sometime later.
Level design changes
Some of the more annoying large maps have been reduced in size. Mood lighting improved for many maps (remember to play in fullscreen, Direct3D mode). Also, aside from the monster population rebalance, there are now several bonus levels associated with the new uberbosses, as well as 8 special uberlevels for high level characters.
In line with the skill changes, the hireable mercenaries feature entirely new skillsets. They have also been beefed up to keep up with the new difficulty. Check out the improved mercenaries here.
This summary is by no means complete, and many of the specifics have been left out. For more detailed information, check out the official FAQ at http://modsbylaz.planetdiablo.gamespy.com/faq.html