I find Gemini to be quite good / acceptable at code review, design, and design review, but it's notably far behind Claude Code for implementation.
Are you having better results?
Codex is fast and decent, but I REALLY have to stay on top of it. The amount of times it makes executive design decisions on the fly to completely break everything is way too high.
I've used it with fairly wide open prompts and also detailed markdown specs and it has no problem making them perfectly, but good code quality requires a bit of follow up work.
I either vibe code a whole personal project, or strongly direct it to generate individual changes. It's fine for both.
The Pro model is the only good model for complex code and I think it's slower than Claude and Codex.