There are two current types of gel nails:

light cured and no-light gels. A gel nail is typically a pre-mixed polymer and monomer gel that is first applied to the nails and then cured under ultra-violet lights. Light cured are still more common, but the advantage to no-light gel nails is less time waiting in the light. There's also the added benefit of not needing that piece of equipment (the light).

No-light gel nails are cured with a special gel activator that is brushed or sprayed onto the nail. Some are cured by being dipped in plain water

• They don’t last as long and are less durable than acrylic, even though they tend to cost more.
• Gel nails are harder to do yourself if you like to do home manicures.
• It’s been noted that nail polish won’t stick to the gel finish as well as it does to an acrylic finish.
• If a gel nail breaks, you may be in for some trouble. It can sometimes be more of a shatter effect than a clean break, so self-fixing a break is not usually an option. You’ll need to make an appointment right away with your manicurist. Sometimes they do break cleanly; basic nail glue could be used in that case.
• Gel nails almost always need to be filed off. You can’t just soak them away.

Reference site: http://skincare.lovetoknow.com/Gel_Nails_Acrylic_Nails