Annoying Arrows: Arrows can come from Archers (duh), Elves, Rangers, Heroes, Towers, Buildings, and even from the sky. Elves and Rangers are by far the worst since they can shoot you from the shadows while being invisible near trees! It gets worse... Arrows can be upgraded into fire arrows, silverthorn arrows, and frost arrows just to make life harder for you on the battlefield.
Best Level Ever: Helm's Deep, Minas Tirith, The Black Gate, Edoras, Isengard (Good side)... The list goes on and on. It's more subjective with the Black Gate & Helm's Deep as they are both well known for being very difficult and frustrating.
Evil Is Cool: Admit it. You wanted to play the evil factions. And who could blame you? The bad guys have some of the coolest stuff in the games — Isengard gets vast legions of Uruk-hai (and the chance to control Saruman); the goblins get to spam hundreds and hundreds ofexpendable troops, paving the way for their dragons; and Mordor...well, they have legions of orcs, trolls, oliphants, and even the Nazgul.
In the second game, you can control Sauron.
The Rise of the Witch-King takes this even further, with Angmar being the focus of the expansion. Angmar gets...some undeniably awesome stuff.
Grenade Spam: Later on in the BFME 1 Evil campaign, Gondor constantly spams Trebuchets.
They Changed It, Now It Sucks: Removing Rohan as a faction quickly became this to many since Rohan was a well liked faction and many were annoyed that they just had their Cavalry added to Gondor and a few heroes likewise.
Likewise, the removal of the "build plot" funcionality was met with a degree of criticism.
Trade Snark: For some unfathomable reason, the default names for the games' installation folders all have trademark signs in them. Even the Start menu / desktop shortcuts have trademark signs in their names.