This is a list of things I look out for in a codebase.
General list of bad practices. You may see the points duplicated else where.
Not being consistent
Not paying attention to commit history
Not isolating work into separate commits
Not following style guides
Committing commented code
Skipping pre commit hooks
Skipping already existing tests without good reasons
A lot of conditions ("if" statements, or "switch" statements)
Logic is not properly structured
Should consider a factory
A lot of hacks