The difference between Hoover SH20030 and S2220 are:
Hoover S2220 vs SH20030
images from manufacturer

Price:
The Hoover SH20030 is a bit more expensive, it is priced at $64.99 whereas the S2220 is priced at $59.99 at hoover.com (prices checked on July 13, 2013)

Edge Cleaning:
The SH20030 features Brushed Edge Cleaning that removes dirt and dust up against edges whereas the S2220 does not.

Height Adjustment:
The S2220 has 3 manual height settings whereas the SH20030 features automatic adjustment.

Filtration:
The SH20030 uses Micro filtration while the S2220 use standard filtration.

Hoover WindTunnel Technology:
The SH20030 features Hoover WindTunnel Technology while the S2220 does not.

Warranty:
The SH20030 is backed up with a 2 year limited warranty while the S2220 carries 1 year limited warranty.

Nozzle Width:
The SH20030 has a nozzle width of 11 inches while the nozzle width on S2220 is 9-inch.

Color:
The SH20030 is grey while the S2220 is red.

Similarities:
They are bagless.
They both have spinning brush and brush on/off switch.
They have 20 ft cable.
120 volts motor.

Read manuals for more details:
SH20030 manual: http://hoover.com/file/642/
S2220 manual: http://hoover.com/file/617/

If you know more difference between Hoover S2220 and SH20030, please share here, thank you.