You might choose to stay the night in Geneva, rather than doing it as a daytrip, but it is possible. The ride is 3.5 hours each way and if you get an early start, you will have plenty of time.
Geneva isn't as scenic as Lucerne but if you happen to have an extra day with nothing to do, it makes for a good activity.
One of the most popular landmarks is the Jet d'Eau. What it is is giant stream of lake water that shoots 120m in the air and uses 500 gallons of water per second. At night, it lights up and is worth a look then as well as in the day.
Geneva also houses the European Headquarters of the United Nations. While we were there, we took a tour of it. I found it a bit boring but my boyfriend didn't mind it. Remember to bring your passport, you will need to leave it with the guards while you are inside the UN.
As Geneva is the birthplace of watch making, it is only natural that they should have a Flower Clock. The numbers and detail of the clock are created with planted flowers. The clock works properly (although I don't know how!) and always seems to have the right time. The Flower Clock boasts the largest second hand in the world and is located at the end of Jardin Anglais.