Regulus is not over powered. Here are a few ways to exploit regulus that I have found.
1.Regulus has relatively low base movement speed, and if people do not get move+ items it is an easy way to close distance fast. Once you are at him make sure you have a slowing ability or a stun and wam bam thank you mam. Dead sniper.
2. His sniping ability takes time to use, so if you are low on HP running back to your base always carry lvl 1 healing pots on you. Use immediately when you are clear to give yourself that boost of HP. Doing this will save your life and make his snipe rather useless when used in this capacity.
3. From my experience his mines are not that great, so he really is a 1 trick pony compaired to other demigods. Late game if farmed he can own, but so can any other hero. IMHO the best counter to him in Unclean beast, who can close the distance fast and has DOTS which eat at his already low HP.
Give it some time before we start shouting Z O M G nerf! I feel that the game is really really balanced for just starting. The only thing I see that needs a bit of a nerf is Vampire lords bite... if it had a longer cooldown it would be perfect, as it stands its almost spamable.