Robert E. Lee was a great general as long as he had room to maneuver and troops to maneuver with. When he didn't have those things, he was considerably less effective.Well, now that's interesting. Lee, who was almost always outnumbered and under equipped, wasn't much of a general because he maneuvered his troops. Suggesting that a general shouldn't maneuver troops is like suggesting that a general shouldn't be a general at all.
Great generals have always maneuvered troops. Hannibal consistently out witted the Romans by moving troops around. Rommel, the wily German general of North Africa, kept the British tied up in knots by pitching his forces hither and fore. Of course, Hannibal's victory at Cannae, one of the bloodiest and most deadly in all of history, kept him "maneuvering" around Italy for 8 more years until finally he just left and the Romans won by default. And Rommel often maneuvered his troops so far around the British that they found themselves in desert with no enemy to fight, Germany kinda losing that whole African campaign anyway. So maybe those aren't good comparisons.
But let's look at it this way. Was Grant a good general? Well, if being drunk in battle is a sign of good leadership, sure! From this quarter's issue of Military History Quarterly:
“I was not long in perceiving that Grant had been drinking heavily,” the newsman later wrote, “and that he was still keeping it up.” Unable to persuade Grant’s aides to intervene, “I then took the general in hand myself, enticed him into his stateroom, locked the room…and commenced throwing bottles of whiskey…into the river.” The reporter eventually convinced Grant to lie down and fanned him to sleep. The general’s drinking continued to be a problem from time to time, but Cadwallader helped manage it, and Grant was grateful. For the remainder of the campaign, the reporter enjoyed all the perks of a member of Grant’s staff.Eventually Vicksburg did fall. Perhaps things would have turned out differently if General John Pemberton had been shit-faced as well.
Ah! But that wasn't against Lee. So what about Lee vs. Grant.
Well, there's the Battle of Cold Harbor which started when Grant maneuvered his troops around Lee's flank giving Grant a great opening. But things went quickly down hill from that point as Grant attempted to assault Lee in a fortified position. The result was probably the most lopsided of the Civil War, Grant losing 13,000 men to Lee's 2,500.
Yes, Lee did end up surrendering to Grant ten months later but not because he was out-generaled. By any length of measure, Lee was the better general.