I am a huge fan of polearms and use them a lot, so here are my pet peeves with them.
For me, the traditional problem with polearms is that in a civilized area you simply don't have one on you most of the time. If you are walking around town, I seriously doubt a PC has a pike or halberd with them. In all but the worst towns, a sword on the hip is pushing it. Apart from the funny looks, walking around with a pike is just really impractical. Fortunately, now D&D is far less focused on forcing people into a particular weapon through expertise etc. You can just carry a quarterstaff or a sword and still be effective.
The other problem is that they excel at second rank fighting, but in a small group, that is best used in tight quarters. Unfortunately, tight quarters is exactly the time a DM might decide to impose disadvantage on many reach weapons. It's a bit hard to swing a poleaxe in a kobold tunnel.
The other issue with second rank fighting is that if you are a fighter, you should be the one taking the hits. If you are standing behind somebody, it probably means the bard or cleric has had to step up and take your place at the front. Reach weapons can be best left for semi-combatants.
Polearm Mastery + Sentinel seems rather broken to many groups. You might want to check with your DM before going down that path. It has inspired some DMs to ban feats, which I don't think is much fun for anybody.
For me, the traditional problem with polearms is that in a civilized area you simply don't have one on you most of the time. If you are walking around town, I seriously doubt a PC has a pike or halberd with them. In all but the worst towns, a sword on the hip is pushing it. Apart from the funny looks, walking around with a pike is just really impractical. Fortunately, now D&D is far less focused on forcing people into a particular weapon through expertise etc. You can just carry a quarterstaff or a sword and still be effective.
The other problem is that they excel at second rank fighting, but in a small group, that is best used in tight quarters. Unfortunately, tight quarters is exactly the time a DM might decide to impose disadvantage on many reach weapons. It's a bit hard to swing a poleaxe in a kobold tunnel.
The other issue with second rank fighting is that if you are a fighter, you should be the one taking the hits. If you are standing behind somebody, it probably means the bard or cleric has had to step up and take your place at the front. Reach weapons can be best left for semi-combatants.
Polearm Mastery + Sentinel seems rather broken to many groups. You might want to check with your DM before going down that path. It has inspired some DMs to ban feats, which I don't think is much fun for anybody.