Orruk Warclans are a top tier army. They can be played in three different ways.

Ironjawz which is your alpha strike list, you charge the enemy turn one and kill them as soon as you can. They have the faction defining ability, "Smashing and Bashing" and "Mighty Destroyers." Smashing and Bashing allows you to fight first with multiple units as long as you kill an entire enemy unit when you activate. Mighty Destroyers lets you move in the hero phase or pile in and attack in the hero phase if you're within range. Almost exclusively melee with only a single caster and ranged attack. Super linear army with easy list building that's in the top 5 bracket at the moment.

Bonesplitterz is a bit of the opposite. They are a more defensive army with some of the fastest movement in the game. The army has the highest army wide wound characteristics of any army in the game. They can reach high save values using magic and have an army wide 6++ ignore wounds. Very versatile, having cavalry, decent ranged units, powerful magic and many other things. They throw a lot of dice in the combat phase, but only have single damage, low/no rend attacks and can be seen as pillow-fisted. The Rogue Idol from Forgeworld is required to make this army competitive. Exploding 6's, meaning when you roll a 6 to hit it translates into 2-4 attacks (depending on buffs) and extremely fast movement are their faction defining abilities. In addition to being able to bypass "ignore wound" and ethereal saves in a particular subfaction. They are a mid-tier army but a hidden gem in the meta. Personally I've won more tournaments with them than I haven't. Very hard to play with above average difficulty on list building.

Big Waagh is the third playstyle. It takes bits and pieces from both Bonesplitterz and Ironjawz and combines them into a single army. They have a slower playstyle than Ironjawz, starting off weak but gaining points that give you extremely powerful passive effects as time goes on based on your list composition. Essentially giving all your units 2 to hit and 2 to wound by turn 2. Then you can spend those points and risk losing the passive benefits to gain an army wide buff that's powerful for one turn. However in Big Waagh you lose Smashing and Bashing. When playing Big Waagh there are traditionally two types of armies people build. One is 95% Ironjawz and a Wurrgog Prophet from Bonesplitterz and the other is 75% Bonesplitterz with a few Hardboyz and a Warchanter. Generally not a good idea to go a 50/50 split. They are also a top tier army, below Ironjawz in win rate.

The final army is Slaves to Darkness, I can't go into depth with them at the moment because something came up, but they are extremely hard to play and build a list for, as well as a mid-tier army.