Unit tests: Review unit tests first. Unit tests are a fantastic way to grasp how code is meant to be used by others and to learn what the expected behavior is. Are there any test gaps that should be there?
Method arguments" Make sure arguments to methods make sense and are validated.
Null References" (Yah yah, we know. Use F# and this goes away. We get it already.) Null references are a bitch and it’s worth looking out for them specifically.
Conventions Consistency" Make sure naming, formatting, etc. follow our conventions and are consistent. I like a codebase that’s fairly consistent so you know what to expect.
Disposables: Make sure disposable things are disposed. Look for usages of resources that should be disposed but are not.
Security: There is a whole threat and mitigation review process that falls under this bucket.
WPF + ReactiveUI
Updating UI: Make sure view model properties are updated on the main scheduler (UI thread). This is because we bind the UI to these properties and the UI can only be updated on the UI thread.
ObserveOn: When kicking off truly async operations, make sure we ObserveOn(RxApp.DeferredScheduler) soon after (related to previous).
Over subscriptions: Make sure we're not over subscribing to deferred observables etc that could lead to multiple operations.