Well I'd say loose joints and chipped paint that is highly noticed in any mode. I think others have already mentioned some of the other things that i don't like so no need to repeat them here.

 

Disproportionate hands and arms, lack of double jointed arms and legs for full range, lack of a visible neck, inability of a figure to look full range up or down, derpy face sculpts

 

if only they had made that collar smaller and lowered the shoulders ! would be almost perfect if they had

 

Newage Megatron who looks fantastic from the front but has a hollow back. There’s a mythological forest spirit here like that and it’s always creeped me out. Off he goes, the spooky bastard.

 

Parts that easily break when you pose or transform the figure.

 

Price !!!

 

Ridiculous pricing.

Lots of the shortcomings mentioned above I can tolerate if the price is reasonable enough, at least once I get the figure, I can try to improve it.
For example, the bad face-sculpt, is pretty much #2 on my list, but for OpenPlay BigSpring, I just replaced it's face.

 

Heresy on a Transformers board: I don't accept Earth vehicle-mode TFs because none of them work with 18th-scale humans, the core of my toy collection.

 

- paint chip on figures especially on the face (Looking at you Fantoys!)
- ratchets that are too wide (looking at you V1 and V2 TE-01 and MT downbeat)
- lack of ankle swivel (looking at you Fortress Maximus)
- super huge backpack (looking at you MP-44)
- indentation for logo (pitfall of many third party figures)
- Chrome that comes off (looking at you MP27 and MP28)
- Crazy price due to deliberate stock control (Fantoys totally guilty of this)

 

Weak face sculpts.
Lack of extra faces. (If the robot has a mouth, I want more expressions)
Paint chips and splashes.
Uncomfortable transformations that require you to bend things or force things to work even if its by design. (MPM prime)
Nubs and pegs in places that are easy to break.

 

Cheap plastic!

 

What do you mea- oh god now I can't unsee that damnit

 

1. Coneheads
2. Cartoon accurate faces (except for Ratchet & Ironhide).
3. Parts that don't lock in securely.
4. Exposed head in alt mode.
5. Hip ratchets that prevent a decent pose. (Armada Unicron for example)

 

#1 by far: Poor face sculpts. As others have said, how good the rest of the figure is doesn't matter if the face looks bad. In contrast, a great face can redeem a figure with other flaws. A lot of early 3P figures were guilty of this.
#2: loose/floppy joints. This is one of the reasons I spent a LOT of time tinkering with my MP-44, using Jarrod's mods to tighten up the hips.
#3: Paint which is doomed to be scraped off through simple transformation/posing. TT and FT are especially bad about this.

 

Superior engineering....That ends up with the figure looking like grenades have exploded over it.

 

Like others have mentioned, the face really makes or breaks the toy. The rest of it could look incredible but its an immediate no no if it has the face of a gremlin (unless you're in the market for a gremlin in which case more power to you).

 

A wise man once said, "anything less than the best is a felony." And that's my philosophy on toys.

 

You know, I can handle little flaws here and there. But dammit, don’t start something you can’t finish.

 

Word to your mother.  

 

Fake chests.