I'm pretty lukewarm on Screamer as well. I'm still glad I bought him and will probably buy Thundercracker and Skywarp too if they happen. I don't hate him as much as some of you, but yeah, there are some serious flaws. I'll rank his 4 (yes 4, bear with me) modes below.
Worst - Jet Mode. Pure trash. Hasbro really phoned it in here. Worse robot undercarriage than Silverbolt. Major flaws in the design and look. The flip down panels on the legs have some clearance issues on mine that don't allow it to tab in fully. I'm not even thinking of the stickers as a negative on this mode, there are too may other problems. Hasbro, have you ever seen a jets landing gear? The rear gear is tippy toes? The front gear is way too far forward, which makes the least sense because there is plenty of room for it to fold out the other way, where it would be in the right place.
Meh - Robot Mode. Just okay, don't hate it, don't love it. I do sort of like the wonky proportions with the Popeye forearms and the skinny thighs going into a giant pair of moon boots.
Good - Torso mode. Neat transformation. I like how the gauntlets cover the combiner pegs for the leg bots. Like many others, I'm calling his combined mode Megascream.
Which brings me to...
Best - Midget mode. I'll call him Miniscream. All the power and mass of a voyager packed into a package that is smaller than a deluxe. Ruthless, vindictive and charming, this is the Tyrion Lannister of this Game of Primes. I love him!!! I am actually going to headcanon him as Miniscream and the son of CW Starscream kind of like Dr. Evil and mini-me. (Warning, if you are doing this mode from the jet mode this mode, pull the legs out, flip the wings, then push the legs back in.)