Who praised them? But I don't know what measure we'd use to determine the general reception of this particular feature. Particularly given that almost all video game journalism is mere marketing. So that's probably not a fruitful point to argue over.

Instead I'll offer the things that I think earn the competitive multiplayer a poor rating.

• No skill or even experience based match making. Too many games are blowouts because all of the level 1 players were put on one team.
• Teams are static once a match lobby has formed. If the teams are poorly balanced they will continue to be forever. Players can't even switch voluntarily. The only remedy is to bail on the lobby and hop into a different random one.
• Classes and weapons are poorly balanced. The Bulwark is a key example of a too strong and not fun design. The Assault class, and melee in general is in a pretty poor state (unless you have an infinite defense shield that lets you walk up to people). Many of the weapon options for the classes are almost unusably weak, so class loadouts tend to be very samey. Grenades are spammy and the shock grenade blind duration is not fun.
• Players are randomly assigned Imperial or Chaos marines. But there is basically no character customization for the Chaos marines, while the Imperial marines have 5 or 6 different sets. Either the enemy team should always appear to be Chaos with their NPC style, or they should have included equivalent Chaos customization.
• Players have minimal control over which game modes they play. It's either 100% random or selecting a single mode. A configurable selection is a common multiplayer feature.
• Map design is bland. This is perhaps a more personal preference, but I find the symmetrical, arcade arenas with no narrative character boring.