If the Earth's axis tilted 45 degrees instead of the current 23.5 degrees, the seasons would be far more pronounced than they are, and the poles would be warmer overall. Earth's axis is responsible for the seasons and is at the perfect angle to the sun to support complex life.
An axial tilt of 45 degrees would bring more heat to bear on the hemisphere facing the sun. More solar radiation would strike the temperate zones and the poles during summer, and the equator would also be affected. During winter, the reverse would occur, with far colder temperatures near the poles.
The cycle of day and night would also be affected. In the summer months of a given hemisphere, more of the planet would be perpetually on the day side, similar to how there are bands near the poles that receive 24 hours of sunlight or nightfall depending on the season.
Earth would experience more severe weather patterns because of more drastic changes in temperature, which causes forceful transfer of hot air to areas where cooler air exists. Hurricanes, tornadoes, thunderstorms and floods would be more severe and cause more damage. Earth's axis being tilted at 45 degrees, therefore, would make life much less likely to thrive.