People think it's always great to be first. Not true. Google was not first to search (can you even remember who was?), Microsoft was not first to desktop apps (or OSes for that matter), YouTube was not first to online-video. Where is Netscape now? Come to think of it, first mover winners tend to be the exception rather than the rule.
The biggest risk of going first is that you are (by definition) entering the unknown, and must make big bets with little information. For a small company, these tend to be make it or break it bets. The laws of probability are against you.
In contrast, the biggest advantage of going later is that the pioneers have already scoped out the territory for you. You can see where the ravines and rapids are that have swallowed the unlucky ones, and (more importantly) you can see where the uncontested hills are. When pioneers go at a market, the bets and assumptions they make typically fix their organization and capabilities in certain ways. This means that they are optimized to solve certain problems and not others, which opens up opportunities for the slow movers. Furthermore, unimaginative competitors tend to compete along the same dimensions. For example, early search engines focused on the prevalent banner-ad system, and Google came in with its revolutionary text-ad and auction-based marketing platform. Netscape wanted to charge for clients, and Microsoft gave IE away for free.
So ask yourself, where are the opportunities in established markets today? What things are taken for granted, but really suck compared to what could be? I will assert that the answers to these questions are endless. Such is the law of innovation.