I've read that the Casio fx-115ES does a great job working with complex numbers, but I haven't found it to be so simple. I am looking for an easy way to convert from rectangular to polar form and back. It also seems to get confused when I try to put expressions involving roots or exponents inside parenthesis. For instance, if I try to enter (3/SQRT2) it wants to put the closing parenthesis inside the square root.

You can perform coordinate conversions in the COMP, STAT, MATRIX and VECTOR Modes.
Angle unit may be in either degree or radian.

To convert from rectangular to polar, (SQRT(2)/2,SQRT(2)/2)

Press [SHIFT] [+] (Pol)
Screen displays Pol(
Type in SQRT2
Use right arrow to move cursor out of radical
Type in /2 [SHIFT] [,]
Type in SQRT2
Use right arrow to move cursor out of radical
Type in /2
Close the right parenthesis
Screen displays Pol (SQRT2 /2, SQRT2 / 2)
Press [=]. Display echoes the command on top line and result in bottom line as r=1, theta =45, (if unit is in degree) or theta = 0.7853981634 if unit is radian.

To convert from polar to rectangular coordinates
Note: You cannot use the answer memory to convert back to rectangular because the calculator will use the r-value only. So you will have to enter the radius AND the angle.

ex: Rec(1,45)
Angle must be in degree
Press [SHIFT][-] (Rec)
Screen display Rec(
Type in 1 [SHIFT] (,) 45 [)] [=]
Calculator displays X=0.7071067812, Y=0.7071067812
If you press the SD key hoping to convert the decimals to radicals, the calculator will not do it.

As to the "confusion", I have found none.
After you finish entering the argument of a square root, use the right arrow to move cursor out of under the root symbol to signify that the argument is complete. If you use a left parenthesis inside the root, you must insert the matching right parenthesis inside the root, then move cursor outside the root.

This is how the calculator behaves, and I am not expressing an opinion on how simple or complicated that is. I assume that to make full use of the calculator capabilities, one has to converse with it, using the syntax it understands.