<p>Does anyone know of a web site where I can find a list of 32-bit MIPS instructions/opcodes, with the following features:</p>
<ul>
<li>Clearly distinguishes between real opcodes and assembly-language macros (pseudo-instructions)</li>
<li>Describes the instruction behavior including differences depending on privilege level.
<li>Indicates in which instruction set revision the instruction was introduced/revised (e.g. MIPS I, MIPS II, MIPS32, etc.)</li>
<li>Includes privileged instructions such as syscall.</li>
</ul>
<p>I am aware of numerous web sites which document &quot;part of&quot; the instruction set, mostly for teaching purposes.  They tend to leave out or only partially describe floating-point and privileged instructions.</p>
<p>In case you're wondering, I'm looking at Verilog code for a MIPS processor subset, and trying to figure out exactly to what extent it complies with the instruction sets of any real MIPS processors!</p>

I can only partially answer the question: I'd recommend
See MIPS Run
by Dominic Sweetman, if you're not already referring to it. I have the first edition of the book, the second edition is now current.
table 8.2 lists each opcode and expected behavior, differentiating assembler macros and  listing the instructions they decompose to. Unfortunately it does not differentiate user vs kernel mode.
table 8.6 lists the ISA level where each instruction was introduced, including obscure variants like the LSI MiniRISC
syscall is present in the table, though lacking much description
The first edition mentions the kernel. supervisor, and user privilege levels but does not discuss what operations are allowed in each. I do not know what changes were made in the second edition.