I assume you are driving. As such, I can't say much about the route or Lom. But we did visit Geiranger and it's fjord and areas nearby.
Geiranger is mostly a tourism hub for those tranferring to & from boats on the fjord. It is small and can be covered on foot in no more than 2 hours - much of that dipping into tourist shops. I would not spend the night there unless you also want to do one of the many hikes that originate there. There are some interesting ones that I wish we had had time to do. We thought the Geirangerfjord was a bit more majestic than the one closer to Bergen that all the "nutshell" tourists see.
When we went we considered renting a car, but read a lot about significant tolls, as well as $10/gal gas. Add to that the difficulty of driving between the fingers of the fjords and we decided against it. Between the fjords, not only do you have to go up & down insanely twisty mountain roads, but crossing water can take 1/2 a day as cars have to cue-up for the ferries, and yet another cost. If you are going to do more than just dip into Geiranger and then back out of fjord country, I would seriously consider NOT driving. Public transport, whether train, bus, boat, or (yes) air, is simple, well organized, likely cheaper than driving, and certainly easier on the driver who now can sit back and enjoy the scenery.
Near Geiranger we also visited Åndalsnes (and took a bus on the "Trollstegen" road to Geiranger - awesome!) and Alesund (lovely small city). That covered our northern fjord experience. From there we went to Bergen for a southern fjord experience. Believe it or not, we decided to fly between Alesund and Bergen even though it's only about 150 miles apart. Because of the fjords in between, the choice was a 11-hour bus ride or a 45 minute flight, and the cost was almost the same! We expected a little shuttle plane and were surprised to find a completely full Boing 727!