For "browsing" the iPad is fine. For intensive use of the web for purposes such as research, there are inherent limitations. About 95% of my internet use is on my desktop or laptop where I have multiple monitors and can have multiple resizable windows on each one. But that is quite different from a user who accesses the web for casual consumption of a single web page at a time. Furthermore, depending upon the web sites you frequent, you may find the absence of support for "flash" in the Safari web browser to be a limitation. Other browsers overcome that limitation to some extent but since there is no way to change your "default" browser on the iPad, that introduces other annoyances.
No one can tell you whether the iPad is adequate for your needs without knowing more about your requirements. In general, if you find that your latop/desktop is overkill for your requirements, the iPad will be a reasonable substitute. On the other hand, if your requirements fall toward the "power user" end of the spectrum, you may find the iPad to be a good complement to your other system(s) (I do.) but you're unlikely to find that it is an adequate substitute.