Extremely challenging after dif 20+, despite the lagging which can be helpful to outmaneuver enemies. The game is simple (simple is good - this applies here) enough but still lags HARD. Go figure....
The main strategy is to simply avoid spikes. They're unreliable and ofter prancing around them anywhere costs a hit (and the streak). Speaking of: the "XXX stars wihout being hit" are quite unforgiving, but all of them are doable before difficulty 20, where things start to get out of control. If going for them it's better to restart if hit because difficulty never resets during a play.
Blue stars give more points the more recent they are. If they're about to blow, they give almost half the points. It's best to dispatch them early as they spend less time on screen, also.
Reaching dif. 30 seems to be the real challenge. Since difficulty only rises when blue stars are defeated and each new dif level requires their own number, to reach level 30 then ~460 blue stars are needed. This may take some serious amount of time.
Overall, great game, but lagging definitely pulls a star. Controls are OK (it's just mouse, after all) and the rest is satisfactory. The dev also took feedback and that's a good thing.