1. team behind the project?
2. type of blockchain?
3. real-world use-cases?
4. partnerships?
4 points above is what I always see before investing in altcoins and besides that I also see whitepaper so that I know more about the objectives of the project
About the whitepaper and i may not try to take the whitepaper as a factor to identify the project. There are so many developers who have been copy paste the whitepaper and even some developers were paying someone to create the whitepaper. It will take a lot of time to do a research with the whitepaper and i will be much more focused with the track record of the team and try to verify whether it's a real or fake person