The rapid kinetics of the reaction of sodium and potassium with water are well explained by the spikes formed and the "Coulomb explosion". But the unexpectedly slow reaction of lithium in water is still a puzzle.
I have watched a small piece of lithium wire (~2 grams) reacting in about 100 mL of water. The reaction is quite rapid at first, then slows down, and then almost stops. The major changes in the system (besides the evolution of hydrogen) are a moderate temperature rise and a pH increase to about 14. Lithium hydroxide is not very soluble (17%, hot). The temperature could not possibly get hot enough to melt lithium (mp = 180 C), whereas sodium melts at 98 C and potassium at 63 C. I watched an irregular piece of sodium (~20 grams) bubble in water (initially cold) until it melted and became globular - just before it exploded!
Lithium is reminiscent of magnesium in water, where magnesium develops a protective oxide/hydroxide coat which inhibits further reaction with water unless the water is very hot. It is worth noting that metals that corrode in water may be inhibited in alkaline media (like iron in concrete). Sodium and potassium are excepted from this inhibition because of the great solubility of their hydroxides and the possibility of melting.
Lithium may start out moderately fast, but slow down as the pH rises, and overall seem a lot slower than sodium or potassium because it will not melt in water and has a solid surface that becomes inhibited by the high pH after some reaction.